0000906709-21-000005 | 10-K | XBRL Viewer

Cover - USD ($)	12 Months Ended
Cover - USD ($)	Dec. 31, 2020	Feb. 17, 2021	Jun. 30, 2020
Document And Entity Information [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	0-24006
Entity Registrant Name	NEKTAR THERAPEUTICS
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	94-3134940
Entity Address, Address Line One	455 Mission Bay Boulevard South
Entity Address, City or Town	San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94158
City Area Code	415
Local Phone Number	482-5300
Title of 12(b) Security	Common Stock, $0.0001 par value
Trading Symbol	NKTR
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 4,100,000,000
Entity Common Stock, Shares Outstanding (in shares)		182,182,063
Documents Incorporated by Reference	Portions of registrant’s definitive Proxy Statement to be filed for its 2020 Annual Meeting of Stockholders are incorporated by reference into Part III hereof. Such Proxy Statement will be filed with the Securities and Exchange Commission within 120 days of the end of the fiscal year covered by this Annual Report on Form 10-K.
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Central Index Key	0000906709

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 198,955	$ 96,363
Short-term investments	862,941	1,228,499
Accounts receivable	38,889	36,802
Inventory	15,292	12,665
Advance payments to contract manufacturers	3,908	31,834
Other current assets	18,020	15,387
Total current assets	1,138,005	1,421,550
Long-term investments	136,662	279,119
Property, plant and equipment, net	59,662	65,665
Operating lease right-of-use assets	126,476	134,177
Goodwill	76,501	76,501
Other assets	1,461	344
Other assets	1,538,767	1,977,356
LIABILITIES AND STOCKHOLDERS’ EQUITY
Senior secured notes, net and interest payable (see Note 5)	0	252,891
Accounts payable	22,139	19,234
Accrued compensation	14,532	11,467
Accrued clinical trial expenses	44,207	32,626
Accrued contract manufacturing expenses	11,310	7,304
Other accrued expenses	9,585	12,338
Operating lease liability, current portion	13,915	12,516
Deferred revenue, current portion	91	5,517
Total current liabilities	115,779	353,893
Operating lease liability, less current portion	136,373	142,730
Liabilities related to the sales of future royalties, net	200,340	72,020
Deferred revenue, less current portion	2,464	2,554
Other long-term liabilities	6,516	768
Total liabilities	461,472	571,965
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares designated, issued or outstanding at December 31, 2020 or 2019	0	0
Common stock, $0.0001 par value; 300,000 shares authorized; 180,091 shares and 176,505 shares issued and outstanding at December 31, 2020 and 2019, respectively	18	17
Capital in excess of par value	3,388,730	3,271,097
Accumulated other comprehensive loss	(2,295)	(1,005)
Accumulated deficit	(2,309,158)	(1,864,718)
Total stockholders’ equity	1,077,295	1,405,391
Total liabilities and stockholders’ equity	$ 1,538,767	$ 1,977,356

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Preferred stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares designated (in shares)	0	0
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	180,091,000	176,505,000
Common stock, shares outstanding (in shares)	180,091,000	176,505,000

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue:
Total revenue	$ 152,915	$ 114,617	$ 1,193,323
Operating costs and expenses:
Cost of goods sold	19,477	21,374	24,412
Research and development	408,678	434,566	399,536
General and administrative	104,682	98,712	81,443
Impairment of assets and other costs for terminated program	45,189	0	0
Total operating costs and expenses	578,026	554,652	505,391
Income (loss) from operations	(425,111)	(440,035)	687,932
Non-operating income (expense):
Interest expense	(6,851)	(21,310)	(21,582)
Non-cash interest expense on liability related to sale of future royalties	(30,267)	(25,044)	(21,196)
Interest income and other income (expense), net	18,282	46,335	37,571
Total non-operating expense, net	(18,836)	(19)	(5,207)
Income (loss) before provision for income taxes	(443,947)	(440,054)	682,725
Provision for income taxes	493	613	1,412
Net income (loss)	$ (444,440)	$ (440,667)	$ 681,313
Net income (loss) per share
Basic ( in dollars per share)	$ (2.49)	$ (2.52)	$ 4.02
Diluted (in dollars per share)	$ (2.49)	$ (2.52)	$ 3.78
Weighted average shares outstanding used in computing net income (loss) per share
Basic (in shares)	178,581	174,993	169,600
Diluted (in shares)	178,581	174,993	180,119
Product sales
Revenue:
Total revenue	$ 17,504	$ 20,117	$ 20,774
Royalty revenue
Revenue:
Total revenue	30,999	41,222	41,976
Non-cash royalty revenue related to sale of future royalties
Revenue:
Total revenue	48,563	36,303	33,308
License, collaboration and other revenue
Revenue:
Total revenue	$ 55,849	$ 16,975	$ 1,097,265

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (444,440)	$ (440,667)	$ 681,313
Other comprehensive income (loss):
Net unrealized gain (loss) on available-for-sale investments	(927)	5,693	(2,975)
Net foreign currency translation gain (loss)	(363)	(382)	(1,230)
Other comprehensive income (loss)	(1,290)	5,311	(4,205)
Comprehensive income (loss)	$ (445,730)	$ (435,356)	$ 677,108

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669619-108580

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8924-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(22))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 11
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22694-107794

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721683-107760

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22595-107794

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 1B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669625-108580

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 11: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(18))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 12: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(20))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Reference 13: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794

Reference 15: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22663-107794

Reference 16: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 28
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612

Reference 17: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599

Reference 18: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22583-107794

Reference 19: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(g)(1)(ii))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 20: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 45
-Paragraph 60B
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121326447&loc=SL5780133-109256

Reference 21: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

Reference 22: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 23: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22658-107794

+ Details

- Definition

Amount after tax and reclassification adjustments of other comprehensive income (loss).

+ References

+ Details

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Capital in Excess of Par Value	Accumulated Other Comprehensive Income/(Loss)	Accumulated Deficit	Accumulated Deficit Cumulative Effect, Period of Adoption, Adjustment
Beginning Balance (in shares) at Dec. 31, 2017			159,524
Beginning Balance at Dec. 31, 2017	$ 87,828	$ 12,577	$ 15	$ 2,207,865	$ (2,111)	$ (2,117,941)	$ 12,577
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)			5,721
Shares issued under equity compensation plans	61,729		$ 1	61,728
Stock-based compensation	88,101			88,101
Sale of stock to Bristol-Myers Squibb (Note 10) (in shares)			8,285
Sale of stock to Bristol-Myers Squibb (Note 10)	790,232		$ 1	790,231
Comprehensive income (loss)	677,108				(4,205)	681,313
Ending Balance (in shares) at Dec. 31, 2018			173,530
Ending Balance at Dec. 31, 2018	1,717,575		$ 17	3,147,925	(6,316)	(1,424,051)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)			2,975
Shares issued under equity compensation plans	23,377			23,377
Stock-based compensation	99,795			99,795
Comprehensive income (loss)	(435,356)				5,311	(440,667)
Ending Balance (in shares) at Dec. 31, 2019			176,505
Ending Balance at Dec. 31, 2019	1,405,391		$ 17	3,271,097	(1,005)	(1,864,718)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)			3,586
Shares issued under equity compensation plans	23,373		$ 1	23,372
Stock-based compensation	94,261			94,261
Comprehensive income (loss)	(445,730)				(1,290)	(444,440)
Ending Balance (in shares) at Dec. 31, 2020			180,091
Ending Balance at Dec. 31, 2020	$ 1,077,295		$ 18	$ 3,388,730	$ (2,295)	$ (2,309,158)

- Definition

Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

+ References + Details

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended			106 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Cash flows from operating activities:
Net income (loss)	$ (444,440,000)	$ (440,667,000)	$ 681,313,000
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Non-cash royalty revenue related to sale of future royalties	(48,563,000)	(36,303,000)	(33,308,000)	$ (255,705,000)
Non-cash interest expense on liability related to sale of future royalties	30,267,000	25,044,000	21,196,000	196,960,000
Stock-based compensation	94,261,000	99,795,000	88,101,000
Depreciation and amortization	14,182,000	13,156,000	10,870,000
Impairment of advance payments to contract manufacturers and equipment for terminated program	20,351,000	0	0
Accretion of premiums (discounts), net and other non-cash transactions	3,943,000	(11,394,000)	(10,952,000)
Changes in operating assets and liabilities
Accounts receivable	1,913,000	6,411,000	(25,505,000)
Inventory	(2,627,000)	(1,284,000)	(655,000)
Operating leases, net	2,743,000	13,090,000	0
Other assets	4,476,000	1,190,000	(31,652,000)
Accounts payable	2,382,000	12,967,000	971,000
Accrued compensation	4,697,000	1,530,000	1,674,000
Other accrued expenses	8,644,000	4,349,000	31,492,000
Deferred revenue	(5,516,000)	(16,565,000)	(15,331,000)
Net cash provided by (used in) operating activities	(313,287,000)	(328,681,000)	718,214,000
Cash flows from investing activities:
Purchases of investments	(987,533,000)	(1,380,865,000)	(2,271,250,000)
Maturities of investments	1,449,304,000	1,614,036,000	890,957,000
Sales of investments	41,700,000	0	11,963,000
Purchases of property, plant and equipment	(7,258,000)	(26,285,000)	(14,239,000)
Sales of property and plant	0	0	2,633,000
Net cash provided by (used in) investing activities	496,213,000	206,886,000	(1,379,936,000)
Cash flows from financing activities:
Issuance of common stock to Bristol-Myers Squibb (Note 10)	0	0	790,231,000
Proceeds from sale of future royalties, net of $3.8 million of transaction costs	146,250,000	0	0
Repayment of senior notes	(250,000,000)	0	0
Proceeds from shares issued under equity compensation plans	23,396,000	23,355,000	61,735,000
Net cash provided by (used in) financing activities	(80,354,000)	23,355,000	851,966,000
Effect of exchange rates on cash and cash equivalents	20,000	(102,000)	(101,000)
Net increase (decrease) in cash and cash equivalents	102,592,000	(98,542,000)	190,143,000
Cash and cash equivalents at beginning of year	96,363,000	194,905,000	4,762,000
Cash and cash equivalents at end of year	198,955,000	96,363,000	194,905,000	$ 198,955,000
Supplemental disclosure of cash flow information:
Cash paid for interest	9,742,000	19,199,000	19,471,000
Cash paid for income taxes	539,000	555,000	618,000
Operating lease right-of-use assets recognized in exchange for lease liabilities	$ 2,133,000	$ 57,691,000	$ 0

Consolidated Statements of Cash Flows (Parenthetical) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Statement of Cash Flows [Abstract]
Sale of future royalties transaction costs	$ 3.8

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Summary of Significant Accounting Policies	Organization and Summary of Significant Accounting Policies Organization We are a research-based biopharmaceutical company headquartered in San Francisco, California and incorporated in Delaware. We are developing a pipeline of drug candidates that utilize our advanced polymer conjugate technology platforms, which are designed to enable the development of new molecular entities that target known mechanisms of action. Our research and development pipeline of new investigational drugs includes investigational treatments for cancer, autoimmune disease and viral infections. Our research and development activities have required significant ongoing investment to date and are expected to continue to require significant investment. As a result, we expect to continue to incur substantial losses and negative cash flows from operations in the future. We have financed our operations primarily through cash generated from licensing, collaboration and manufacturing agreements and financing transactions. At December 31, 2020, we had approximately $1.2 billion in cash and investments in marketable securities. On April 13, 2020, we repaid the principal and accrued interest of our senior notes totaling $254.8 million. See Note 5 for additional information. Basis of Presentation, Principles of Consolidation and Use of Estimates Our Consolidated Financial statements include the financial position, results of operations and cash flows of our wholly-owned subsidiaries: Inheris Biopharma, Inc. (Inheris), Nektar Therapeutics (India) Private Limited (Nektar India) and Nektar Therapeutics UK Limited. We have eliminated all intercompany accounts and transactions in consolidation. Our Consolidated Financial Statements are denominated in U.S. dollars. Accordingly, changes in exchange rates between the applicable foreign currency and the U.S. dollar will affect the translation of each foreign subsidiary’s financial results into U.S. dollars for purposes of reporting our consolidated financial results. We include translation gains and losses in accumulated other comprehensive loss in the stockholders’ equity section of our Consolidated Balance Sheets. To date, such cumulative currency translation adjustments have not been significant to our consolidated financial position. Our comprehensive income (loss) consists of our net income (loss) plus our foreign currency translation gains and losses and unrealized holding gains and losses on available-for-sale securities. There were no significant reclassifications out of accumulated other comprehensive loss to the statements of operations during the years ended December 31, 2020, 2019 and 2018. The preparation of consolidated financial statements in conformity with U.S. generally accepted accounting principles (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Accounting estimates and assumptions are inherently uncertain. Actual results could differ materially from those estimates and assumptions. Our estimates include those related to the selling prices of performance obligations and amounts of variable consideration in collaboration agreements, royalty revenue, and other assumptions required for revenue recognition as described further below; the net realizable value of inventory; the impairment of investments, goodwill and long-lived assets; contingencies, accrued clinical trial, contract manufacturing and other expenses; non-cash royalty revenue and non-cash interest expense from our liabilities related to our sales of future royalties; assumptions used in stock-based compensation; and ongoing litigation, among other estimates. We base our estimates on historical experience and on other assumptions that management believes are reasonable under the circumstances. These estimates form the basis for making judgments about the carrying values of assets and liabilities when these values are not readily apparent from other sources. As appropriate, we assess estimates each period, update them to reflect current information, and will generally reflect any changes in estimates in the period first identified. Reclassifications Certain items previously reported in specific financial statement captions have been reclassified to conform to the current period presentation. Such reclassifications do not materially impact previously reported revenue, operating loss, net loss, total assets, liabilities or stockholders’ equity. Fair Value of Financial Instruments The recorded amounts of certain financial instruments, including cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities. Investments that are classified as available-for-sale are recorded at estimated fair value. The disclosed fair value related to our cash equivalents and investments is based on market prices from a variety of industry standard data providers and generally represent quoted prices for similar assets in active markets or have been derived from observable market data. Cash, Cash Equivalents, and Investments in Marketable Securities We consider all investments in marketable securities with an original maturity of three months or less when purchased to be cash equivalents. We classify investments in securities with remaining maturities of less than one year, or where our intent is to use the investments to fund current operations or to make them available for current operations, as short-term investments. We classify investments in securities with remaining maturities of over one year as long-term investments. Investments are designated as available-for-sale and are carried at fair value with unrealized gains and losses reported in stockholders’ equity as accumulated other comprehensive income loss. We review our portfolio of available-for-sale debt securities, using both quantitative and qualitative factors, to determine if declines in fair value below amortized cost have resulted from a credit-related loss or other factors. If the decline in fair value is due to credit-related factors, we recognize a loss in our Consolidated Statement of Operations, whereas if the decline in fair value is not due to credit-related factors, we recognize the loss in other comprehensive income (loss). We include coupon interest on securities classified as available-for-sale, as well as amortization of premiums and accretion of discounts to maturity, in interest income. The cost of securities sold is based on the specific identification method. Our cash, cash equivalents, short-term investments and long-term investments are exposed to credit risk in the event of default by the third parties that hold or issue such assets. Our cash, cash equivalents, short-term investments and long-term investments are held or issued by financial institutions that management believes are of high credit quality. Our investment policy limits investments to fixed income securities denominated and payable in U.S. dollars such as corporate bonds, corporate commercial paper, U.S. government obligations, and money market funds and places restrictions on maturities and concentrations by type and issuer. For our available-for-sale securities, we have significant concentrations of issuers in the banking and financial services industry. While our investment policy requires that we only invest in highly-rated securities and limit our exposure to any single issuer, the COVID-19 pandemic may materially affect the financial condition of issuers. Additionally, pursuant to our investment policy, we may sell securities before maturity if the issuer’s credit rating has been downgraded below our minimum credit rating requirements, which may result in a loss on the sale. As a result of the COVID-19 pandemic, we have seen credit downgrades for certain of our securities. Accordingly, if the COVID-19 pandemic or other factors result in downgrades below our minimum credit rating requirements and if we decide to sell these securities, we may experience losses on such sales. Accounts Receivable and Significant Customer Concentrations Our customers are primarily pharmaceutical and biotechnology companies that are primarily located in the U.S. and Europe and with whom we have multi-year arrangements. Our accounts receivable balance contains billed and unbilled trade receivables from product sales, milestones (to the extent that they have been achieved and are due from the counterparty), other contingent payments and royalties, as well as reimbursable costs from collaborative research and development agreements. For the year ended December 31, 2020, our accounts receivable included $38.7 million for unbilled net expense reimbursements from our collaboration partner Bristol-Myers Squibb Company (BMS) and $0.2 million under customer contracts from our collaboration partners. For the year ended December 31, 2019, our accounts receivable included $24.0 million for unbilled net expense reimbursements from BMS and $12.8 million from customer contracts, which included our estimate of $11.6 million for royalties resulting from net sales of MOVANTIK®, ADYNOVATE® and REBINYN® during the three months ended December 31, 2019. Since we sold our rights to receive royalties in the 2020 Purchase and Sale Agreement with Healthcare Royalty Management, LLC, as discussed further in Note 7, we did not record accounts receivable for these royalties at December 31, 2020. We generally do not require collateral from our partners. We perform a regular review of our partners’ credit risk and payment histories when circumstances warrant, including payments made subsequent to year-end. When appropriate, we provide for an allowance for doubtful accounts by reserving for specifically identified doubtful accounts, although historically we have not experienced credit losses from our accounts receivable. At December 31, 2019, three different partners represented 65%, 17% and 14%, respectively, of our accounts receivable. Inventory and Significant Supplier Concentrations We generally manufacture inventory upon receipt of firm purchase orders from our collaboration partners, and we may manufacture certain intermediate work-in-process materials and purchase raw materials based on purchase forecasts from our collaboration partners. Inventory includes direct materials, direct labor, and manufacturing overhead, and we determine cost on a first-in, first-out basis for raw materials and on a specific identification basis for work-in-process and finished goods. We value inventory at the lower of cost or net realizable value, and we write down defective or excess inventory to net realizable value based on historical experience or projected usage. We expense inventory related to our research and development activities when we purchase or manufacture it. Before the regulatory approval of our drug candidates, we recognize research and development expense for the manufacture of drug products that could potentially be available to support the commercial launch of our drug candidates, if approved. We are dependent on our suppliers and contract manufacturers to provide raw materials and drugs of appropriate quality and reliability and to meet applicable contract and regulatory requirements. In certain cases, we rely on single sources of supply of one or more critical materials. Consequently, in the event that supplies are delayed or interrupted for any reason, including as a result of the COVID-19 pandemic, our ability to develop and produce our drug candidates, our ability to supply comparator drugs for our clinical trials, or our ability to meet our supply obligations could be significantly impaired, which could have a material adverse effect on our business, financial condition and results of operations. Leases On January 1, 2019, we adopted Accounting Standards Codification (ASC) 842, Leases (ASC 842). ASC 842 supersedes the guidance in ASC 840, Leases (ASC 840). Under ASC 842, an entity recognizes a right-of-use asset and a corresponding lease liability, measured as the present value of the lease payments. In our adoption, we used the package of practical expedients, which, among other things, allowed us to carry forward our historical lease classification of those leases in effect as of January 1, 2019. We present results for the year ended December 31, 2020 and 2019 under ASC 842. We have not restated the results for the year ended December 31, 2018 continue to report them under ASC 840. We determine if an arrangement contains a lease at the inception of the arrangement. Right-of-use assets represent our right to use an underlying asset for the lease term, and lease liabilities represent our obligation to make lease payments arising from the lease. We recognize operating lease right-of-use assets and liabilities at the lease commencement date based on the present value of lease payments over the expected lease term. In determining the present value of lease payments, we use our incremental borrowing rate based on the information available at the lease commencement date. However, in determining the present value of our lease payments for leases in effect when we adopted ASC 842, we used our incremental borrowing rate as of January 1, 2019. We have elected the practical expedient to account for the lease and non-lease components, such as common area maintenance charges, as a single lease component for our facilities leases, and elected the short-term lease recognition exemption for our short-term leases, which allows us not to recognize lease liabilities and right-of-use assets for leases with an original term of twelve months or less. Our expected lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise any such options. We recognize lease expense for our operating leases on a straight-line basis over the expected lease term. We have elected to recognize lease incentives, such as tenant improvement allowances, at the lease commencement date as a reduction of the right-of-use asset and lease liability until paid to us by the lessor to the extent that the lease provides a specified fixed or maximum level of reimbursement and we are reasonably certain to incur reimbursable costs at least equaling such amounts. For leases in effect as of January 1, 2019, we recognized our lease incentives as part of our transition adjustment. Please see Note 6 for additional information regarding our leases. Long-Lived Assets We state property, plant and equipment at cost, net of accumulated depreciation. We capitalize major improvements and expense maintenance and repairs as incurred. We generally recognize depreciation on a straight-line basis. We depreciate manufacturing, laboratory and other equipment over their estimated useful lives of generally three to ten years, depreciate buildings over the estimated useful life of generally twenty years and amortize leasehold improvements over the shorter of the estimated useful lives or the remaining term of the related lease. Goodwill represents the excess of the price paid for another entity over the fair value of the assets acquired and liabilities assumed in a business combination. We are organized in one reporting unit and evaluate the goodwill for the Company as a whole. Goodwill has an indefinite useful life and is not amortized, but instead tested for impairment at least annually in the fourth quarter of each year using an October 1 measurement date. We assess the impairment of long-lived assets whenever events or changes in business circumstances indicate that the carrying amounts of the assets may not be fully recoverable. In the case of property, plant and equipment and right-of-use assets for our leases, we determine whether there has been an impairment by comparing the carrying value of the asset to the anticipated undiscounted net cash flows associated with the asset. If such cash flows are less than the carrying value, we write down the asset to its fair value, which may be measured as anticipated discounted net cash flows associated with the asset. In the case of goodwill impairment, we compare the carrying value of the reporting unit to its fair value, which we generally measure using market capitalization for our single reporting unit. If an impairment exists, we write down goodwill such that the carrying value of the reporting units equals its fair value. Collaborative Arrangements We enter into collaboration arrangements with pharmaceutical and biotechnology collaboration partners, under which we may grant licenses to our collaboration partners to further develop and commercialize one of our proprietary drug candidates, either alone or in combination with the collaboration partners’ compounds, or grant licenses to partners to use our technology to research and develop their own proprietary drug candidates. We may also perform research, development, manufacturing and supply activities under our collaboration agreements. Consideration under these contracts may include an upfront payment, development and regulatory milestones and other contingent payments, expense reimbursements, royalties based on net sales of approved drugs, and commercial sales milestone payments. Additionally, these contracts may provide options for the customer to purchase our proprietary PEGylation materials, drug candidates or additional contract research and development services under separate contracts. When we enter into collaboration agreements, we assess whether the arrangements fall within the scope of ASC 808, Collaborative Arrangements (ASC 808) based on whether the arrangements involve joint operating activities and whether both parties have active participation in the arrangement and are exposed to significant risks and rewards of the arrangement. To the extent that the arrangement falls within the scope of ASC 808, we assess whether the payments between us and our collaboration partner fall within the scope of other accounting literature. If we conclude that payments from the collaboration partner to us represent consideration from a customer, such as license fees and contract research and development activities, we account for those payments within the scope of ASC 606, Revenue from Contracts with Customers (ASC 606). However, if we conclude that our collaboration partner is not a customer for certain activities and associated payments, such as for certain collaborative research, development, manufacturing and commercial activities, we present such payments as a reduction of research and development expense or general and administrative expense, based on where we present the underlying expense. Revenue Recognition For elements of those arrangements that we determine should be accounted for under ASC 606, we assess which activities in our collaboration agreements are performance obligations that should be accounted for separately and determine the transaction price of the arrangement, which includes the assessment of the probability of achievement of future milestones and other potential consideration. For arrangements that include multiple performance obligations, such as granting a license or performing contract research and development activities or participation on joint steering or other committees, we allocate upfront and milestone payments under a relative standalone selling price method. Accordingly, we develop assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. These key assumptions may include revenue forecasts, clinical development timelines and costs, discount rates and probabilities of clinical and regulatory success. Product sales Product sales are primarily derived from manufacturing and supply agreements with our customers. We have assessed our current manufacturing and supply arrangements and have generally determined that they provide the customer an option to purchase our proprietary PEGylation materials. Accordingly, we treat each purchase order as a discrete exercise of the customer’s option (i.e. a separate contract) rather than as a component of the overall arrangement. The pricing for the manufacturing and supply is generally at a fixed price and may be subject to annual producer price index (PPI) adjustments. We invoice and recognize product sales when title and risk of loss pass to the customer, which generally occurs upon shipment. Customer payments are generally due 30 days from receipt of invoice. We test our products for adherence to technical specifications before shipment; accordingly, we have not experienced any significant returns from our customers. Royalty revenue Generally, for our collaboration arrangements that include sales-based royalties, we have granted our collaboration partner a license to our intellectual property. Pursuant to these arrangements, our collaboration partners are typically obligated to pay a royalty that is based on the net sales of their approved drugs that are sold in the countries where we have intellectual property rights covering their drugs. As of December 30, 2020, we have sold our rights to receive sales-based royalties for CIMZIA®, MIRCERA®, MOVANTIK®, ADYNOVATE® and REBINYN® as further described in Note 7. For collaboration arrangements that include sales-based royalties, we have concluded that the license is the predominant item to which the royalties relate, which include commercial milestone payments based on the level of sales. Accordingly, we recognize royalty revenue, including for our non-cash royalties, when the underlying sales occur based on our best estimates of sales of the drugs. Our partners generally pay royalties or commercial milestones after the end of the calendar quarter in accordance with contractual terms. We present commercial milestone payments within license, collaboration and other revenue. License, collaboration and other revenue License Grants: For collaboration arrangements that include a grant of a license to our intellectual property, we consider whether the license grant is distinct from the other performance obligations included in the arrangement. Generally, we would conclude that the license is distinct if the customer is able to benefit from the license with the resources available to it. For licenses that are distinct, we recognize revenues from nonrefundable, upfront payments and other consideration allocated to the license when the license term has begun and we have provided all necessary information regarding the underlying intellectual property to the customer, which generally occurs at or near the inception of the arrangement. Milestone Payments: At the inception of the arrangement and at each reporting date thereafter, we assess whether we should include any milestone payments or other forms of variable consideration in the transaction price, based on whether a significant reversal of revenue previously recognized is not probable upon resolution of the uncertainty. Since milestone payments may become payable to us upon the initiation of a clinical study, filing for or receipt of regulatory approval or the first commercial sale of a product, we review the relevant facts and circumstances to determine when we should update the transaction price, which may occur before the triggering event. When we do update the transaction price for milestone payments, we allocate it on a relative standalone selling price basis and record revenue on a cumulative catch-up basis, which results in recognizing revenue for previously satisfied performance obligations in such period. If we update the transaction price before the triggering event, we recognize the increase in the transaction price as a contract asset. Our partners generally pay development milestones subsequent to achievement of the triggering event. Research and Development Services: For amounts allocated to our research and development obligations in a collaboration arrangement, we recognize revenue over time using a proportional performance model, representing the transfer of goods or services as we perform activities over the term of the agreement. Shipping and Handling Costs We recognize costs related to shipping and handling of product to customers in cost of goods sold. Research and Development Expense Research and development costs are expensed as incurred and include salaries, benefits and other operating costs such as outside services, supplies and allocated overhead costs. We perform research and development for our proprietary drug candidates and technology development and for certain third parties under collaboration agreements. For our proprietary drug candidates and our internal technology development programs, we invest our own funds without reimbursement from a third party. Where we perform research and development activities under a joint development collaboration, such as our collaboration with BMS, we record the cost reimbursement from our partner as a reduction to research and development expense when reimbursement amounts are due to us under the agreement. We record an accrued expense for the estimated costs of our clinical trial activities performed by third parties. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows to our vendors. Payments under the contracts depend on factors such as the achievement of certain events, successful enrollment of patients, and completion of certain clinical trial activities. We generally accrue costs associated with the start-up and reporting phases of the clinical trials ratably over the estimated duration of the start-up and reporting phases. We generally accrue costs associated with the treatment phase of clinical trials based on the estimated activities performed by third parties. We may also accrue expenses based on the total estimated cost of the treatment phase on a per patient basis and expense the per patient cost ratably over the estimated patient treatment period based on patient enrollment in the trials. In specific circumstances, such as for certain time-based costs, we recognize clinical trial expenses using a methodology that we consider to be more reflective of the timing of costs incurred. We record an accrued expense for the estimated costs of our contract manufacturing activities performed by third parties. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows to our vendors. Payments under the contracts include upfront payments and milestone payments, which depend on factors such as the achievement of the completion of certain stages of the manufacturing process. For purposes of recognizing expense, we assess whether we consider the production process is sufficiently defined such that the resulting product can be considered the delivery of a good, as evidenced by predictive or contractually required yields in the production process or payment terms based on the actual yield, or the delivery of a service, where processes and yields are developing and less certain. If we consider the process to be the delivery of a good, we recognize expense when the drug product is delivered, or we otherwise bear risk of loss. If we consider the process to be the delivery of a service, we recognize expense based on our best estimates of the contract manufacturer’s progress towards completion of the stages in the contracts. We recognize and amortize upfront payments and accrue liabilities based on the specific terms of each arrangement. Certain arrangements may provide upfront payments for certain stages of the arrangement and milestone payments for the completion of certain stages, and, accordingly, we may record advance payments for services that have not been completed or goods not delivered and liabilities for stages where the contract manufacturer is entitled to a milestone payment. We capitalize advance payments for goods or services that will be used or rendered for future research and development activities and recognize expense as the related goods are delivered or services performed. We base our estimates on the best information available at the time. However, additional information may become available to us in the future which may allow us to make a more accurate estimate in future periods. In this event, we may be required to record adjustments to research and development expenses in future periods when the actual level of activity becomes more certain. We generally consider such increases or decreases in cost as changes in estimates and reflect them in research and development expenses in the period identified. Impairment of Assets and Other Costs for Terminated Program On January 14, 2020, the joint FDA Anesthetic Drug Products Advisory Committee and Drug Safety and Risk Management Committee did not recommend approval of our NDA for NKTR-181. As a result, we withdrew our NDA and decided to make no further investments in this program. On February 26, 2020, the Audit Committee of our Board of Directors approved management’s plan for the wind-down of Inheris and the NKTR-181 program. As a result, in the three months ended March 31, 2020, we wrote off $19.7 million of advance payments to contract manufacturers for commercial batches of NKTR-181. We also incurred $25.5 million of additional costs, primarily for non-cancellable commitments to our contract manufacturers and certain severance costs. We present these costs in the Impairment of assets and other costs for terminated program line in our Consolidated Statement of Operations. We did not incur any substantial costs related to the wind-down of Inheris and the NKTR-181 program after March 31, 2020. As of December 31, 2020, we have substantially completed our wind-down and do not expect to incur additional costs. Stock-Based Compensation Stock-based compensation arrangements include grants of stock options, restricted stock units (RSUs) and performance stock units (PSUs) under our equity incentive plans, as well as shares issued under our Employee Stock Purchase Plan (ESPP), through which employees may purchase our common stock at a discount to the market price. We expense the grant date fair value of options, RSUs and PSUs on a straight-line basis over the requisite service periods in our Consolidated Statements of Operations and recognize forfeitures of options, RSUs and PSUs as they occur. For options and RSUs that vest upon the achievement of performance milestones, we estimate the vesting period based on our evaluation of the probability of achievement of each respective milestone and the related estimated date of achievement. We recognize stock-based compensation expense for purchases under the ESPP over the respective six-month purchase period. We report expense amounts in cost of goods sold, research and development expense, and general and administrative expense based on the function of the applicable employee. Stock-based compensation charges are non-cash charges and have no effect on our reported cash flows. We estimate the grant date fair value of our stock-based compensation awards as follows: •We use the Black-Scholes option pricing model for the respective grant to determine the estimated fair value of the option on the date of grant (grant date fair value) and the estimated fair value of common stock purchased under the ESPP. The Black-Scholes option pricing model requires the input of highly subjective assumptions, including but not limited to, our stock price volatility over the term of the awards, and actual and projected employee stock option exercise behaviors. Because our employee stock options have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models may not provide a reliable single measure of the fair value of our employee stock options or common stock purchased under the ESPP. •The number of shares issuable under PSUs is based on our total shareholder return as compared to other companies within the Nasdaq biotechnology index over the measurement period and may be capped based on our absolute total shareholder return over such period. We use the Monte Carlo simulation model to determine the estimated grant date fair value. The Monte Carlo simulation model incorporates assumptions such as the volatility of our stock, the volatility of the stock of other peer companies within the index, and the correlation of both our stock and our peer companies’ stock to the index. •The fair value of an RSU is equal to the closing price of our common stock on the grant date. Management will continue to assess the assumptions and methodologies used to calculate the estimated fair value of stock-based compensation. Circumstances may change and additional data may become available over time, which could result in changes to these assumptions and methodologies, and which could materially impact our fair value determination. Net Income (Loss) Per Share For all periods presented in the Consolidated Statements of Operations, the net income (loss) available to common stockholders is equal to the reported net income (loss). We calculate basic net income (loss) per share based on the weighted-average number of common shares outstanding during the periods presented and calculate diluted net income (loss) per share based on the weighted-average number of shares of common stock outstanding, including potentially dilutive securities, which consist of common shares underlying stock options and RSUs. For the years ended December 31, 2020 and 2019, basic and diluted net loss per share are the same due to our net losses and the requirement to exclude potentially dilutive securities which would have an antidilutive effect on net loss per share. We excluded weighted average outstanding stock options and RSUs totaling 17.4 million and 17.9 million for the years ended December 31, 2020 and 2019, respectively. For the year ended December 31, 2018, the effect of these dilutive securities under the treasury stock method was approximately 10.5 million, and we excluded approximately 3.3 million of weighted-average shares of common stock underlying outstanding stock options from the computation of diluted net income per share because their effect was antidilutive. Income Taxes We account for income taxes under the liability method. Under this method, we determine deferred tax assets and liabilities based on differences between the financial reporting and tax reporting bases of assets and liabilities, measured using enacted tax rates and laws that we expect to be in effect when we expect the differences to reverse. Realization of deferred tax assets is dependent upon future earnings, the timing and amount of which are uncertain. We record a valuation allowance against deferred tax assets to reduce their carrying value to an amount that is more likely than not to be realized. When we establish or reduce the valuation allowance related to the deferred tax assets, our provision for income taxes will increase or decrease, respectively, in the period we make such determination. We utilize a two-step approach to recognize and measure uncertain tax positions. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates that it is more likely than not that the position will be sustained upon tax authority examination, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount of benefit, determined on a cumulative probability basis, that is more than 50% likely of being realized upon ultimate settlement. Comprehensive Income (Loss) Comprehensive income (loss) is the change in stockholders’ equity from transactions and other events and circumstances other than those resulting from investments by stockholders and distributions to stockholders. Our other comprehensive income (loss) includes net income (loss), gains and losses from the foreign currency translation of the assets and liabilities of our India and UK subsidiaries, and unrealized gains and losses on investments in available-for-sale securities. Coronavirus Aid, Relief, and Economic Security (CARES) Act In March 2020, the U.S. government enacted the CARES Act, which includes modifications to the limitation on business interest expense and net operating loss provisions and provides a payment delay of employer payroll taxes during 2020 after the date of enactment. The CARES Act has not had a material effect on our results of operations or financial position. Recently Adopted Accounting Pronouncements On January 1, 2020, we adopted Accounting Standards Update 2018-18: Clarifying the Interaction between Topic 808 and Topic 606 (ASU 2018-18). The guidance clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer for a promised good or service that is distinct within the collaborative arrangement. The guidance also precludes entities from presenting amounts related to transactions with a collaborative arrangement participant that is not a customer as revenue, unless those transactions are directly related to third-party sales. ASU 2018-18 is applied retrospectively to January 1, 2018, when we adopted ASC 606. Our adoption of ASU 2018-18 did not materially affect our revenue recognition. On January 1, 2020, we adopted ASU 2016-13: Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The guidance modifies the measurement and recognition of credit losses for most financial assets and certain other instruments. The amendment updates the guidance for measuring and recording credit losses on financial assets measured at amortized cost by replacing the “incurred loss” model with an “expected loss” model. As a result of adoption, we present these financial assets, which include our accounts receivable and available-for-sale debt securities, at the net amount we expect to collect. The amendment also requires that we record credit losses related to available-for-sale debt securities as an allowance through net income rather than reducing the carrying amount under the historical, other-than-temporary-impairment model. Our adoption of ASU 2016-13 did not materially affect our Consolidated Financial Statements. Recent Accounting Pronouncements We have reviewed other recent accounting pronouncements and concluded they are either not applicable to us or that we do not expect adoption to have a material effect on our consolidated financial statements.

Cash and Investments in Marketable Securities

12 Months Ended

Dec. 31, 2020

Cash and Cash Equivalents [Abstract]

Cash and Investments in Marketable Securities

Cash and investments in marketable securities, including cash equivalents, are as follows (in thousands):


	Estimated Fair Value at
	December 31, 2020		December 31, 2019
Cash and cash equivalents	$	198,955	$	96,363
Short-term investments	862,941		1,228,499
Long-term investments	136,662		279,119
Total cash and investments in marketable securities	$	1,198,558	$	1,603,981

We invest in liquid, high quality debt securities. Our investments in debt securities are subject to interest rate risk. To minimize the exposure due to an adverse shift in interest rates, we invest in securities with maturities of two years or less and maintain a weighted average maturity of one year or less. All of our long-term investments as of December 31, 2020 and 2019 had maturities between one and two years.

During the year ended December 31, 2020 and 2018, we sold available-for-sale securities totaling $41.7 million and $12.0 million, respectively. Gross realized gains and losses on those sales were not significant. During the year ended December 31, 2019, we did not sell any of our available-for-sale securities. The cost of securities sold is based on the specific identification method.

We report our accrued interest receivable, which totaled $5.1 million and $6.5 million at December 31, 2020 and December 31, 2019, respectively, in other current assets on our Consolidated Balance Sheets.

Our portfolio of cash and investments in marketable securities includes (in thousands):


	Fair Value Hierarchy Level	December 31, 2020								December 31, 2019
		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value		Fair Value
Corporate notes and bonds	2	$	686,543	$	1,035	$	(109)	$	687,469	$	1,132,182
Corporate commercial paper	2	313,520		44		(67)		313,497		375,473
Obligations of U.S. government agencies	2	2,380		2		—		2,382		—
Available-for-sale investments		1,002,443		1,081		(176)		1,003,348		1,507,655
Money market funds	1							179,302		83,546
Certificate of deposit	N/A							9,623		6,951
Cash	N/A							6,285		5,829
Total cash and investments in marketable securities								$	1,198,558	$	1,603,981

_______________________________________________________________

Level 1 — Quoted prices in active markets for identical assets or liabilities.

Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices for identical or similar assets or liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. We use a market approach to value our Level 2 investments. The disclosed fair value related to our investments is based on market prices from a variety of industry standard data providers and generally represents quoted prices for similar assets in active markets or has been derived from observable market data. For the years ended December 31, 2020 and 2019, there were no transfers between Level 1 and Level 2 of the fair value hierarchy.

Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.

At December 31, 2019, our gross unrealized gains and losses totaled $2.1 million and $0.3 million, respectively.

At December 31, 2020 and 2019, we had letter of credit arrangements in favor of our landlords and certain vendors totaling $8.1 million and $6.8 million, respectively. These letters of credit are secured by investments of similar amounts.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Inventory

12 Months Ended

Dec. 31, 2020

Inventory Disclosure [Abstract]

Inventory

Inventory consists of the following (in thousands):


	December 31,
	2020		2019
Raw materials	$	2,422	$	1,673
Work-in-process	10,703		8,267
Finished goods	2,167		2,725
Total inventory	$	15,292	$	12,665

Property, Plant and Equipment

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Property, plant and equipment consists of the following (in thousands):


	December 31,
	2020		2019
Building and leasehold improvements	$	92,977	$	93,097
Laboratory equipment	40,121		36,623
Computer equipment and software	28,684		26,910
Manufacturing equipment	21,796		22,030
Furniture, fixtures, and other	9,872		9,662
Depreciable property, plant and equipment at cost	193,450		188,322
Less: accumulated depreciation	(138,488)		(127,875)
Depreciable property, plant and equipment, net	54,962		60,447
Construction-in-progress	4,700		5,218
Property, plant and equipment, net	$	59,662	$	65,665

Building and leasehold improvements include our manufacturing, research and development and administrative facilities and the related improvements to these facilities. Laboratory and manufacturing equipment include assets that support both our manufacturing and research and development efforts. Construction-in-progress includes assets being built to enhance our manufacturing and research and development efforts.

Depreciation and amortization expense on property, plant and equipment for the years ended December 31, 2020, 2019, and 2018 was $12.5 million, $11.0 million, and $8.8 million, respectively.

Senior Secured Notes	12 Months Ended
Senior Secured Notes	Dec. 31, 2020
Debt Disclosure [Abstract]
Senior Secured Notes	Senior Secured Notes On October 5, 2015, we completed the sale and issuance of $250.0 million in aggregate principal amount of 7.75% senior secured notes due 2020 (the Notes). The Notes were secured by a first-priority lien on substantially all of our assets (except our right-of-use assets) and bore interest at a rate of 7.75% per annum payable in cash quarterly in arrears on January 15, April 15, July 15, and October 15 of each year. Interest was calculated based on actual days outstanding over a 360 days year. The Notes were to mature on October 5, 2020, at which time the outstanding principal would have been due and payable. In connection with the issuance of the Notes, we paid fees and expenses of $8.9 million, of which $8.7 million of transaction and facility fees paid directly to the purchasers of the Notes and other direct issuance costs were recorded as a discount to the senior secured notes, net liability balance in our Consolidated Balance Sheet. On April 13, 2020, we redeemed the Notes at par and therefore repaid the principal of $250.0 million and accrued interest of $4.8 million. As a result of the redemption and repayment, the liens discussed above were terminated.

Leases

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Leases

Operating Leases

Our leases consist of a Lease Agreement (the Mission Bay Lease) with ARE-San Francisco No. 19, LLC (ARE) for our 153,203 square foot corporate office and R&D facility located at 455 Mission Bay Boulevard, San Francisco, California (the Mission Bay Facility) and a Lease Agreement (the Third Street Lease) with Kilroy Realty Finance Partnership, L.P. (Kilroy) for an additional 135,936 square foot facility to support our R&D operations at 360 Third Street, San Francisco, California (the Third Street Facility). The following table presents key information regarding these leases (dollars in thousands):


	Mission Bay Facility		Third Street Facility
Lease commencement	September 2017		June 2018
Lease term	January 2030		January 2030
Space delivered during the year ended December 31, 2019
Square footage	13,907		67,105
Right-of-use asset and lease liability recognized	$	6,698	$	50,993
Space delivered during the year ended December 31, 2020
Square footage	4,940		—
Right-of-use asset and lease liability recognized	$	2,133	$	—
Renewal terms	Two consecutive five-year terms		One five-year term

•The monthly base rent for both facilities will escalate over the term of the lease at various intervals.

•Both leases include various covenants, indemnities, defaults, termination rights, security deposits and other provisions customary for lease transactions of this nature.

•During the term of the Mission Bay Lease, we are responsible for paying our share of operating expenses specified in the lease, including utilities, common area maintenance, insurance costs and taxes.

•For the Third Street Lease, our fixed annual base rent on an industrial gross lease basis includes certain expenses and property taxes paid directly by the landlord. We have a one-time right of first offer with respect to certain additional rental space at the Third Street Facility.

We recognize rent expense for these operating leases on a straight-line basis over the lease period. The components of lease costs, which we include in operating expenses in our Consolidated Statements of Operations, were as follows (in thousands):


	Year Ended December 31,
	2020		2019		2018
Operating lease cost	$	18,985	$	14,697	$	7,972
Variable lease cost	8,179		6,408		4,497
Total lease costs	$	27,164	$	21,105	$	12,469

During the year ended December 31, 2020 and 2019, we recorded operating lease expense of $19.0 million and $14.7 million, respectively, and paid $16.2 million and $8.4 million, respectively, of operating lease payments related to our lease liabilities, which we include in net cash provided by (used in) operating activities in our Consolidated Statements of Cash Flows.

As of December 31, 2020, the maturities of our operating lease liabilities were as follows (in thousands):


Year ending December 31,
2021	$	17,938
2022	20,141
2023	20,780
2024	21,439
2025	22,117
2026 and thereafter	97,764
Total lease payments	200,179
Less: portion representing interest	(46,380)
Less: lease incentives	(3,511)
Operating lease liabilities	150,288
Less: current portion	(13,915)
Operating lease liabilities, less current portion	$	136,373

As of December 31, 2020, the weighted-average remaining lease term is 9.1 years and the weighted-average discount rate used to determine the operating lease liability was 5.9%.

Liabilities Related to the Sales of Future Royalties

12 Months Ended

Dec. 31, 2020

On February 24, 2012, we entered into a purchase and sale agreement (the 2012 Purchase and Sale Agreement) with RPI Finance Trust (RPI), an affiliate of Royalty Pharma, pursuant to which we sold, and RPI purchased, our right to receive royalty payments (the 2012 Transaction Royalties) arising from the worldwide net sales, from and after January 1, 2012, of (a) CIMZIA®, under our license, manufacturing and supply agreement with UCB Pharma (UCB), and (b) MIRCERA®, under our license, manufacturing and supply agreement with F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (together referred to as Roche). We received aggregate cash proceeds of $124.0 million for the 2012 Transaction Royalties. As part of this sale, we incurred approximately $4.4 million in transaction costs, which we will amortize to interest expense over the estimated life of the 2012 Purchase and Sale Agreement. Although we sold all of our rights to receive royalties from the CIMZIA® and MIRCERA® products, as a result of our ongoing manufacturing and supply obligations related to the generation of these royalties, we continue to account for these royalties as revenue. We recorded the $124.0 million in proceeds from this transaction as a liability (the 2012 Royalty Obligation) that is amortized using the interest method over the estimated life of the 2012 Purchase and Sale Agreement as royalties from the CIMZIA® and MIRCERA® products are remitted directly to RPI.

On December 16, 2020, we entered into a purchase and sale agreement (the 2020 Purchase and Sale Agreement) with entities managed by Healthcare Royalty Management, LLC (collectively, HCR). Pursuant to the 2020 Purchase and Sale Agreement, we agreed to sell to HCR certain of our rights to receive royalty payments (the 2020 Transaction Royalties) arising from the worldwide net sales, from and after October 1, 2020 until such time certain return thresholds are met as described below, of (a) MOVANTIK® under that certain License Agreement, dated September 20, 2009, by and between Nektar and AstraZeneca AB, as amended, (b) ADYNOVATE® under that certain Exclusive Research, Development, License and Manufacturing and Supply Agreement, dated September 26, 2005, by and among Nektar, Baxalta US Inc. and Baxalta GmbH, as amended, (c) REBINYN® under that certain Settlement and License Agreement, dated December 21, 2016, by and among Nektar, Novo Nordisk Inc., Novo Nordisk A/S and Novo Nordisk A/G and (d) licensed products under that certain Right to Sublicense Agreement, dated October 27, 2017, by and among Nektar, Baxter Incorporated, Baxalta US Inc. and Baxalta GmbH.

The 2020 Purchase and Sale Agreement will automatically expire, and the payment of the 2020 Transaction Royalties to HCR will cease, when HCR has received payments of the 2020 Transaction Royalties equal to $210.0 million (the 2025 Threshold), if the 2025 Threshold is achieved on or prior to December 31, 2025, or $240.0 million, if the 2025 Threshold is not achieved on or prior to December 31, 2025 (or, if earlier, the date on which the last royalty payment under the relevant license agreements is made). If HCR has received payments of the 2020 Transaction Royalties equal to at least $208.0 million on or prior to December 31, 2025, we have the option to pay the difference between the 2025 Threshold and such 2020 Transaction Royalties, and the 2025 Threshold will be met and the 2020 Purchase and Sale Agreement will expire. After the 2020 Purchase and Sale Agreement expires, all rights to receive the 2020 Transaction Royalties return to Nektar.

On December 30, 2020, we received aggregate cash proceeds of $150.0 million for the 2020 Transaction Royalties. As part of the sale, we incurred approximately $3.8 million in transaction costs, which will be amortized to interest expense over the estimated life of the 2020 Purchase and Sale Agreement. Although we sold all of our rights to receive royalties from these

products, as a result of the limits on the 2020 Transaction Royalties to be received by HCR and our ongoing manufacturing and supply obligations related to the generation of these royalties, we will continue to account for these non-cash royalties as revenue, commencing with royalties for the three months ended December 31, 2020, to be received by HCR in the first quarter of 2021. We recorded the $150.0 million in proceeds from this transaction as a liability (the 2020 Royalty Obligation) that will be amortized using the effective interest method over the estimated life of the 2020 Purchase and Sale Agreement. We did not recognize any non-cash interest expense from closing on December 30, 2020 to December 31, 2020 as any imputed interest was immaterial.

The following table shows the activity within the liability account during the year ended December 31, 2020 and for the period from the inception of the 2012 Purchase and Sale Agreement on February 24, 2012 (inception) and the 2020 Purchase and Sale Agreement on December 30, 2020 to December 31, 2020 (in thousands):


	Year-Ended December 31, 2020						Period from inception to December 31, 2020
	2012 Purchase and Sale Agreement		2020 Purchase and Sale Agreement		Total		2012 Purchase and Sale Agreement		2020 Purchase and Sale Agreement		Total
Liability related to the sale of future royalties—beginning balance	$	73,551	$	—	$	73,551	$	—	$	—	$	—
Royalty monetization proceeds	—		150,000		150,000		124,000		150,000		274,000
Non-cash royalty revenue	(37,938)		(10,625)		(48,563)		(245,080)		(10,625)		(255,705)
Non-cash interest expense	30,267		—		30,267		196,960		—		196,960
Payments to RPI	—		—		—		(10,000)		—		(10,000)
Liability related to the sale of future royalties – ending balance	65,880		139,375		205,255		65,880		139,375		205,255
Less: unamortized transaction costs	(1,165)		(3,750)		(4,915)		(1,165)		(3,750)		(4,915)
Liability related to the sale of future royalties, net	$	64,715	$	135,625	$	200,340	$	64,715	$	135,625	$	200,340

Pursuant to the 2012 Purchase and Sale Agreement, in March 2014 and March 2013, we were required to pay RPI $7.0 million and $3.0 million, respectively, as a result of worldwide net sales of MIRCERA® for the 12 month periods ended December 31, 2013 and 2012 not reaching certain minimum thresholds. The 2012 Purchase and Sale Agreement does not include any other potential payments related to minimum net sales thresholds and, therefore, we do not expect to make any further payments to RPI related to this agreement.

As royalties are remitted to RPI and HCR by our licensees, the balances of the respective Royalty Obligations will be effectively repaid over the lives of the agreements. To determine the amortization of the Royalty Obligations, we are required to estimate the total amount of future royalty payments to be received by RPI and HCR, respectively. The sum of these amounts less the net proceeds we received will be recorded as non-cash interest expense over the lives of the respective Royalty Obligations. We periodically assess the estimated royalty payments to RPI and HCR from our licensees and to the extent the amount or timing of such payments is materially different than our original estimates, we will prospectively adjust the imputed interest rate and the related amortization of the appropriate Royalty Obligation.

There are a number of factors that could materially affect the amount and timing of royalty payments from our licensees, most of which are not within our control. Such factors include, but are not limited to, changing standards of care, the introduction of competing products, manufacturing or other delays, biosimilar competition, intellectual property matters, adverse events that result in governmental health authority imposed restrictions on the use of the drug products, significant changes in foreign exchange rates as the royalties remitted to RPI or HCR are made in U.S. dollars (USD) while significant portions of the underlying sales of the products of our licensees are made in currencies other than USD, and other events or circumstances that could result in reduced royalty payments from our licensees, all of which would result in a reduction of non-cash royalty revenues and the non-cash interest expense over the life of the respective Royalty Obligation. Conversely, for the 2012 Purchase and Sale Agreement, if sales of these products are more than expected, the non-cash royalty revenues and the non-cash interest expense recorded by us would be greater over the term of the 2012 Royalty Obligation.

The following table presents our estimates of the annual interest rates over the lives of the agreements and the resulting prospective interest rates used to recognize non-cash interest expense for the years ended December 31, 2020, 2019 and 2018.


	2012 Purchase and Sale Agreement						2020 Purchase and Sale Agreement
	Year-Ended December 31,						Year-Ended December 31,
	2020		2019		2018		2020
Interest rates - end of period presented
Implicit interest rate over the life of the agreement	20.2	%	19.5	%	18.7	%	16.0	%
Prospective effective interest rate	48.0	%	38.0	%	29.0	%	16.0	%

In addition, the 2012 and 2020 Purchase and Sale Agreements grant RPI and HCR, respectively, the right to receive certain reports and other information relating to the 2012 and 2020 Transaction Royalties, respectively, and contains other representations and warranties, covenants and indemnification obligations that are customary for transactions of this nature. To our knowledge, we are currently in compliance with these provisions of the 2012 and 2020 Purchase and Sale Agreements; however, if we were to breach our obligations, we could be required to pay damages to RPI and HCR, respectively, that are not limited to the purchase prices we received in the sale transactions. However, the time limitation we have to indemnify RPI with respect to any breach of these intellectual property-based representations and warranties has passed.

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Purchase Commitments In the normal course of business, we enter into various firm purchase commitments related to contract manufacturing, clinical development and certain other items. As of December 31, 2020, these commitments were approximately $8.0 million, all of which we expect to pay in 2021. Legal Matters From time to time, we are involved in lawsuits, arbitrations, claims, investigations and proceedings, consisting of intellectual property, commercial, employment and other matters, which arise in the ordinary course of business. We make provisions for liabilities when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. Such provisions are reviewed at least quarterly and adjusted to reflect the impact of settlement negotiations, judicial and administrative rulings, advice of legal counsel, and other information and events pertaining to a particular case. Litigation is inherently unpredictable. If any unfavorable ruling were to occur in any specific period, there exists the possibility of a material adverse impact on the results of our operations of that period and on our cash flows and liquidity. On October 30, 2018, we and certain of our executives were named in a putative securities class action complaint filed in the U.S. District Court for the Northern District of California (U.S. District Court in California), which complaint was subsequently amended on May 15, 2019. Also, on February 13, 2019, and February 18, 2019, shareholder derivative complaints were filed in the U.S. District Court for the District of Delaware naming the CEO, CFO and certain members of our board of directors. These class action and shareholder derivative actions assert, among other things, that for a period beginning at least from November 11, 2017 through October 2, 2018, our stock was inflated due to alleged misrepresentations about the efficacy and safety of bempegaldesleukin. On December 30, 2020, the U.S. District Court in California granted Nektar’s motion to dismiss all claims in this securities class action filing, and denied plaintiffs with the ability to file a further amended complaint. Following the motion to dismiss, on January 29, 2021, the class action plaintiffs filed a Notice to Appeal to appeal the district court’s decision to the U.S. Court of Appeals for the Ninth Circuit. In addition, on August 19, 2019, we and certain of our executives were named in a putative securities class action complaint filed in U.S. District Court in California, which complaint was subsequently amended on January 24, 2020. Also, on February 11, 2020, and on February 20, 2020, shareholder derivative complaints were filed in U.S. District Court in California naming the CEO, CFO and certain members of our board of directors, which derivative complaints were consolidated and subsequently amended on July 1, 2020. The class action and shareholder derivative complaints assert, among other things, that for a period between February 15, 2019 and August 8, 2019, inclusive, our stock was inflated due to an alleged failure to disclose a reduction in the planned number of bempegaldesleukin clinical trials and a bempegaldesleukin manufacturing issue. On January 26, 2021, the U.S. District Court in California granted Nektar’s motion to dismiss all claims in this securities class action filing, stating (among other things) that “Defendants’ open disclosure of risks associated with trial delay … suggests that they acted openly with investors.” Following the motion, the class action plaintiffs have an opportunity to file in early March a further amended complaint and the case remains pending. On February 9, 2021, certain of our current and past directors and executives were named in a shareholder derivative complaint filed in the Court of Chancery of the State of Delaware. Allegations in this matter are similar to those raised in the putative securities class action complaints filed on October 30, 2018 and August 19, 2019 in the U.S. District Court in California. All of the securities class action lawsuits and derivative complaints are in the early stages. Accordingly, we cannot reasonably estimate a potential future loss or a range of potential future losses. However, an unfavorable resolution could potentially have a material adverse effect on our business, financial condition, and results of operations or prospects, and potentially result in paying monetary damages. We have recorded no liability for these matters in our Consolidated Balance Sheets at either December 31, 2020 or December 31, 2019. Foreign Operations We operate in a number of foreign countries. As a result, we are subject to numerous local laws and regulations that can result in claims made by foreign government agencies or other third parties that are often difficult to predict even after the application of good faith compliance efforts. Indemnification Obligations During the course of our normal operating activities, we have agreed to certain contingent indemnification obligations as further described below. The term of our indemnification obligations is generally perpetual. There is generally no limitation on the potential amount of future payments we could be required to make under these indemnification obligations. To date, we have not incurred significant costs to defend lawsuits or settle claims based on our indemnification obligations. If any of our indemnification obligations is triggered, we may incur substantial liabilities. Because the aggregate amount of any potential indemnification obligation is not a stated amount, we cannot reasonably estimate the overall maximum amount of any such obligations. We have recorded no liabilities for these obligations on our Consolidated Balance Sheets as of December 31, 2020 or December 31, 2019. Indemnifications in Connection with Commercial Agreements As part of our collaboration agreements with our partners related to the license, development, manufacture and supply of drugs and PEGylation materials based on our proprietary technologies and drug candidates, we generally agree to defend, indemnify and hold harmless our partners from and against third party liabilities arising out of the agreement, including product liability (with respect to our activities) and infringement of intellectual property to the extent the intellectual property is developed by us and licensed to our partners. The term of these indemnification obligations is generally perpetual any time after execution of the agreement. There is generally no limitation on the potential amount of future payments we could be required to make under these indemnification obligations. From time to time, we enter into other strategic agreements such as divestitures and financing transactions pursuant to which we are required to make representations and warranties and undertake to perform or comply with certain covenants, including our obligations to RPI and HCR described in Note 7. In the event it is determined that we breached certain of the representations and warranties or covenants made by us in any such agreements or certain express indemnification provisions are applicable, we could incur substantial indemnification liabilities depending on the timing, nature, and amount of any such claims. To date, we have not incurred costs to defend lawsuits or settle claims related to these indemnification obligations, representations or warranties. Because the aggregate amount of any potential indemnification obligation is not a stated amount, we cannot reasonably estimate the overall maximum amount of any such obligations. We have recorded no liabilities for these obligations in our Consolidated Balance Sheets at either December 31, 2020 or December 31, 2019. Indemnification of Underwriters and Initial Purchasers of our Securities In connection with our sale of equity and senior secured debt securities, we have agreed to defend, indemnify and hold harmless our underwriters or initial purchasers, as applicable, as well as certain related parties from and against certain liabilities, including liabilities under the Securities Act of 1933, as amended. Director and Officer Indemnifications As permitted under Delaware law, and as set forth in our Certificate of Incorporation and our Bylaws, we indemnify our directors, executive officers, other officers, employees, and other agents for certain events or occurrences that may arise while in such capacity. The maximum potential amount of future payments we could be required to make under this indemnification is unlimited; however, we have insurance policies that may limit our exposure and may enable us to recover a portion of any future amounts paid. Assuming the applicability of coverage, the willingness of the insurer to assume coverage, and subject to certain retention, loss limits and other policy provisions, we believe any obligations under this indemnification would not be material, other than retention of up to $10.0 million per incident for merger and acquisition related claims, $10.0 million per incident for securities related claims and $10.0 million per incident for non-securities related claims per our insurance policy. However, no assurances can be given that the covering insurers will not attempt to dispute the validity, applicability, or amount of coverage without expensive litigation against these insurers, in which case we may incur substantial liabilities as a result of these indemnification obligations.

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2020
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Common Stock As discussed in Note 10, on April 3, 2018, we completed the issuance and sale of 8,284,600 shares of our common stock under a Share Purchase Agreement with BMS. These shares are unregistered and subject to certain lock-up and stand-still provisions for a five-year period. Equity Compensation Plans At December 31, 2020, we had approximately 29,784,000 reserved shares of common stock, all of which are reserved for issuance under our equity compensation plans, of which approximately 20,894,000 shares may be issued upon the exercise of outstanding options or the vesting of restricted stock units (RSUs) or performance stock units, approximately 7,569,000 shares are available for grant under our 2017 Performance Incentive Plan and approximately 1,321,000 shares are available for grant under our Employee Stock Purchase Plan. 2017 Performance Incentive Plan Our 2017 Performance Incentive Plan (2017 Plan) was adopted by our board of directors (Board of Directors) on March 28, 2017 and was approved by our stockholders on June 14, 2017. On the date of approval, any shares of our common stock that were available for issuance under our 2012 Performance Incentive Plan (2012 Plan) ceased to be available for future grants. However, options and restricted stock units granted under the 2012 Plan remained outstanding. Subject to the terms of the 2017 Plan, 8,300,000 shares of our common stock, reduced by the number of shares of common stock subject to awards granted under the 2012 Plan on or after March 31, 2017 and prior to the adoption of the 2017 Plan, were initially available for awards under the 2017 Plan. On June 26, 2018, our stockholders approved an amendment to the 2017 Plan whereby 10,900,000 additional shares were made available for award grants under the 2017 Plan (Amended Plan). On June 17, 2020, the stockholders of Nektar approved an amendment to the Amended Plan to increase the aggregate number of shares of Common Stock authorized for issuance thereunder by 10,000,000 shares (Amended and Restated 2017 Plan). Shares issued in respect of any “full-value award” granted under the 2017 Plan will be counted against the share limit described above as 1.5 shares for every one share actually issued in connection with the award. Shares that are subject to or underlie awards which expire or for any reason are cancelled or terminated, are forfeited, fail to vest, or for any other reason are not paid or delivered under the 2017 Plan or the 2012 Plan will again be available for subsequent awards under the 2017 Plan (with any such shares subject to full-value awards increasing the 2017 Plan’s share limit based on the full-value award ratio described above). Notwithstanding the foregoing, shares that are exchanged by a participant or withheld by us to pay the exercise price of an option granted under the 2017 Plan, as well as any shares exchanged or withheld to satisfy the tax withholding obligations related to any award, will not be available for subsequent awards under the 2017 Plan. The purpose of the current Amended and Restated 2017 Plan and our other incentive plans is to promote our success by providing an additional means for us to attract, motivate, retain and reward directors, officers, employees, and other eligible persons through the grant of awards. Equity-based awards are also intended to further align the interests of award recipients and our stockholders. The Amended and Restated 2017 Plan authorizes stock options, stock appreciation rights, stock bonuses, restricted stock, performance stock, stock units, phantom stock or similar rights to purchase or acquire shares, and other forms of awards granted or denominated in our common stock or units of our common stock, as well as cash bonus awards. Members of the Board of Directors, officers or employees, certain consultants and advisors and our subsidiaries are eligible to receive awards under the Amended and Restated 2017 Plan. Pursuant to the Amended and Restated 2017 Plan, we have granted or issued non-qualified stock options, RSUs and PSUs to employees, officers, and non-employee directors. The requisite service period for stock options granted to our employees under the Amended and Restated 2017 Plan as well as our prior plans is generally four years; the requisite service period for stock options granted to our directors is generally one year. The requisite service period for RSUs and PSUs granted under the Amended and Restated 2017 Plan and our prior plans is generally three years for employees and one year for directors. The Amended and Restated 2017 Plan will terminate on March 27, 2027, unless earlier terminated by the Board of Directors. The maximum term of a stock option or stock appreciation right under the Amended and Restated 2017 Plan and our prior plans is eight years from the date of grant. The per share exercise price of an option generally may not be less than the fair market value of a share of our common stock on the NASDAQ Stock Market on the date of grant. Employee Stock Purchase Plan In February 1994, our Board of Directors adopted the Employee Stock Purchase Plan (ESPP) pursuant to section 423(b) of the Internal Revenue Code of 1986. Under the ESPP, 2,500,000 shares of our common stock were originally authorized for issuance. On June 17, 2020, the stockholders of Nektar approved an amendment and restatement of the Amended and Restated Employee Stock Purchase Plan to increase the aggregate number of shares of Common Stock authorized for issuance under the plan by 1,000,000 shares. The terms of the ESPP provide eligible employees with the opportunity to acquire an ownership interest in Nektar through participation in a program of periodic payroll deductions for the purchase of our common stock. Employees may elect to enroll or re-enroll in the ESPP on a semi-annual basis. Stock is purchased at 85% of the lower of the closing price on the first day of the enrollment period or the last day of the enrollment period. 401(k) Retirement Plan We sponsor a 401(k) retirement plan whereby eligible employees may elect to contribute up to the lesser of 60% of their annual compensation or the statutorily prescribed annual limit allowable under Internal Revenue Service regulations. The 401(k) plan permits us to make matching contributions on behalf of all participants, up to a maximum of $6,000 per participant. For the years ended December 31, 2020, 2019, and 2018, we recognized $3.5 million, $3.5 million, and $2.8 million, respectively, of compensation expense in connection with our 401(k) retirement plan. Change in Control Severance Plan On December 6, 2006, our Board of Directors approved a Change of Control Severance Benefit Plan (CIC Plan). This CIC Plan has subsequently been amended a number of times by our Board of Directors with the most recent amendment occurring on April 5, 2011. The CIC Plan is designed to make certain benefits available to our eligible employees in the event of a change of control of Nektar and, following such change of control, an employee’s employment with us or a successor company is terminated in certain specified circumstances. We adopted the CIC Plan to support the continuity of the business in the context of a change of control transaction. The CIC Plan was not adopted in contemplation of any specific change of control transaction. Under the CIC Plan, in the event of a change of control of Nektar and a subsequent termination of employment initiated by us or a successor company other than for Cause (as defined in the CIC Plan) or initiated by the employee for a Good Reason Resignation (as defined in the CIC Plan) in each case within twelve months following a change of control transaction, (i) the Chief Executive Officer would be entitled to receive cash severance pay equal to 24 months base salary plus annual target incentive pay, the extension of employee benefits over this severance period and the full acceleration of unvested outstanding equity awards, and (ii) our Senior Vice Presidents and Vice Presidents (including Principal Fellows) would each be entitled to receive cash severance pay equal to twelve months base salary plus annual target incentive pay, the extension of employee benefits over this severance period and the full acceleration of unvested outstanding equity awards. In the event of a change of control of Nektar and a subsequent termination of employment initiated by the Company or a successor company other than for Cause within twelve months following a change of control transaction, all other employees would each be entitled to receive cash severance pay equal to 6 months base salary plus a pro-rata portion of annual target incentive pay, the extension of employee benefits over this severance period and the full acceleration of each such employee’s unvested outstanding equity awards. Under the CIC Plan, as amended, non-employee directors would also be entitled to full acceleration of vesting of all outstanding stock awards in the event of a change of control transaction.

License and Collaboration Agreements

12 Months Ended

Dec. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

License and Collaboration Agreements

License and Collaboration Agreements We have entered into various collaboration agreements including license agreements and collaborative research, development and commercialization agreements with various pharmaceutical and biotechnology companies. Under these

collaboration arrangements, we are entitled to receive license fees, upfront payments, milestone and other contingent payments, royalties, sales milestone payments, and payments for the manufacture and supply of our proprietary PEGylation materials and/or reimbursement for research and development activities. We generally include our costs of performing these services in research and development expense, except for costs for product sales to our collaboration partners which we include in cost of goods sold. We analyze our agreements to determine whether we should account for the agreements within the scope of ASC 808, and, if so, we analyze whether we should account for any elements under ASC 606.

In accordance with our collaboration agreements, we recognized license, collaboration and other revenue as follows (in thousands):


		Year Ended December 31,
Partner	Agreement	2020		2019		2018
Bristol-Myers Squibb	Bempegaldesleukin	$	50,000	$	—	$	1,059,768
Eli Lilly and Company	NKTR-358	1,259		7,019		11,634
Amgen, Inc.	Neulasta®	4,167		5,000		5,000
Baxalta Incorporated / Takeda	Hemophilia, including ADYNOVATE® and ADYNOVI®	346		378		20,328
Other		77		4,578		535
License, collaboration and other revenue		$	55,849	$	16,975	$	1,097,265

For the years ended December 31, 2020, 2019 and 2018, we recognized $129.6 million, $77.5 million and $95.3 million of revenue for performance obligations that we had satisfied in prior periods, respectively. For all years, the amount includes all of our royalty revenue and non-cash royalty revenue. For the year ended December 31, 2020, the amount includes $50.0 million in BMS Collaboration milestones received.

The following table presents the changes in our deferred revenue balance from our collaboration agreements during the year ended December 31, 2020 (in thousands):


	For the year ended December 31, 2020
Deferred revenue—December 31, 2019	$	8,071
Recognition of previously unearned revenue	(5,516)
Deferred revenue—December 31, 2020	$	2,555

Our balance of deferred revenue contains the transaction price from our collaboration agreements allocated to performance obligations which are partially unsatisfied.

As of December 31, 2020, our collaboration agreements with partners included potential future payments for development milestones totaling approximately $1.7 billion, including amounts from our agreements with BMS and Eli Lilly and Company described below. In addition, under our collaboration agreements we are entitled to receive other contingent payments, including contingent sales milestones and royalty payments, as described below.

There have been no material changes to our collaboration agreements for the year ended December 31, 2020, except as described below.

Bristol-Myers Squibb (BMS): Bempegaldesleukin (previously referred to as NKTR-214)

On February 13, 2018, we entered into a Strategic Collaboration Agreement (the BMS Collaboration Agreement) and a Share Purchase Agreement with BMS, both of which became effective on April 3, 2018. Pursuant to the BMS Collaboration Agreement, we and BMS are jointly developing bempegaldesleukin, including, without limitation, in combination with BMS’s Opdivo®, and other compounds of BMS, us or any third party. The parties have agreed to jointly commercialize bempegaldesleukin on a worldwide basis. We retained the right to record all worldwide sales for bempegaldesleukin. We will share global commercialization profits and losses with BMS for bempegaldesleukin, with Nektar sharing 65% and BMS sharing 35% of the net profits and losses. The parties share the internal and external development costs for bempegaldesleukin in combination regimens based on each party’s relative ownership interest in the compounds included in the regimens. In accordance with the agreement, the parties share development costs for bempegaldesleukin in combination with Opdivo®, 67.5% of costs to BMS and 32.5% to Nektar. The parties share costs for the manufacturing of bempegaldesleukin, 35% of costs to BMS and 65% to Nektar.

The BMS Collaboration Agreement superseded and replaced the Clinical Trial Agreement we entered into with BMS in September 2016 to develop bempegaldesleukin in combination with Opdivo®. Under the Clinical Trial Agreement, we acted as the sponsor of each Combination Therapy Trial and BMS was responsible for 50% of all out-of-pocket costs reasonably incurred in connection with third party contract research organizations, laboratories, clinical sites and institutional review boards. We recorded cost reimbursement payments to us from BMS as a reduction to research and development expense. Each party was otherwise responsible for its own internal costs, including internal personnel costs, incurred in connection with each Combination Therapy Trial.

Upon the effective date of the BMS Collaboration Agreement in April 2018, BMS paid us a non-refundable upfront cash payment of $1.0 billion. We are eligible to receive additional cash payments up to a total of approximately $1.455 billion (including the milestones which we have received under Amendment No. 1 described below) upon the achievement of certain development and regulatory milestones and up to a total of $350.0 million upon the achievement of certain sales milestones. In April 2018, BMS also purchased 8,284,600 shares of our common stock pursuant to the Share Purchase Agreement for total additional cash consideration of $850.0 million.

On January 9, 2020, we and BMS entered into Amendment No. 1 (the Amendment) to the BMS Collaboration Agreement. Pursuant to the Amendment, we and BMS agreed to update the Collaboration Development Plan under which we are collaborating and developing bempegaldesleukin. The cost sharing under the Amendment remains unchanged. We received a non-refundable, creditable milestone payment of $25.0 million for the first patient, first visit in the registrational muscle-invasive bladder cancer trial, which was achieved on January 30, 2020, and also received a non-refundable, non-creditable milestone payment of $25.0 million for the first patient, first visit in the registrational adjuvant melanoma trial, which we achieved on July 27, 2020. For the creditable milestone, BMS is entitled to deduct the amount paid from future development milestones due to us under the original agreement.

BMS has the right, at its sole discretion, to terminate co-funding its share of the development costs for the adjuvant melanoma collaboration study if the metastatic melanoma collaboration study fails to meet the primary endpoint of progression free survival. If BMS exercises such right, we have the right, in our sole discretion, to continue the adjuvant melanoma study.

We determined that the BMS Collaboration Agreement falls within the scope of ASC 808. As mentioned above, BMS shares certain percentages of development costs incurred by us and we share certain percentages of development costs incurred by BMS. We consider these activities to represent collaborative activities under ASC 808 and we recognize such cost sharing proportionately with the performance of the underlying services. We recognize BMS’ reimbursement of our expenses as a reduction of research and development expense and our reimbursement of BMS’ expenses as research and development expense. For the years ended December 31, 2020, 2019 and 2018, we recorded $128.2 million and $105.4 million and $62.5 million, respectively, as a reduction of research and development expenses for BMS’ share of our expenses, net of our share of BMS’ expenses. As of December 31, 2020 and 2019, we have recorded an unbilled receivable of $38.7 million and $24.0 million, respectively, from BMS in accounts receivable in our Consolidated Balance Sheet.

Our share of development costs is limited to an annual cap of $125.0 million. To the extent this annual cap is exceeded, BMS reimburses us for the excess, but we recognize our full share of the research and development expense and recognize the reimbursement as a liability. We repay the liability to the extent that our share of development costs are less than the annual cap in a future year, or by reducing a portion of our share of net profits following the first commercial sale of bempegaldesleukin, if approved. For the year-ended December 31, 2020, our share of the development costs totaled $129.0 million, thereby exceeding the annual cap by $4.0 million. Accordingly, we have recognized $4.0 million for BMS’ reimbursement of the excess over the annual cap in our unbilled billed receivable of $38.7 million, and, due to the repayment provision, we have recognized a liability of $4.0 million in Other long-term liabilities.

We analogized to ASC 606 for the accounting for our two performance obligations, consisting of the delivery of the licenses to develop and commercialize bempegaldesleukin and our participation on joint steering and other collaboration committees. We determined that our committee participation is not material.

During 2018, we aggregated the total consideration of $1.85 billion received under the agreements and allocated it between the stock purchase and the revenue-generating elements, because we and BMS negotiated the agreements together and the effective date of the BMS Collaboration Agreement was dependent upon the effective date of the Share Purchase Agreement. We recorded the estimated fair value of the shares of $790.2 million in stockholders’ equity. We allocated the remaining $1,059.8 million to the transaction price of the collaboration agreement, which we recognized in 2018. We consider the future potential development, regulatory and sales milestones of up to approximately $1.8 billion to be variable consideration.

During the year ended December 31, 2020, we recognized $25.0 million for the achievement of the first patient, first visit in the registrational muscle-invasive bladder cancer trial and $25.0 million for the achievement of the first patient, first visit in the registrational adjuvant melanoma trial. We continue to exclude the other milestones from the transaction price as of December 31, 2020 due to the significant uncertainties involved with clinical development and regulatory approval. We re-evaluate the transaction price at each reporting period and as uncertain events are resolved or other changes in circumstances occur.

Eli Lilly and Company (Lilly): NKTR-358

On July 23, 2017, we entered into a worldwide license agreement with Eli Lilly and Company (Lilly), which became effective on August 23, 2017, to co-develop NKTR-358, a novel immunological drug candidate that we invented. Under the terms of the agreement, we (i) received an initial payment of $150.0 million in September 2017 and are eligible for up to $250.0 million in additional development milestones, (ii) will co-develop NKTR-358 with Lilly, for which we were responsible for completing Phase 1 clinical development and certain drug product development and supply activities, (iii) will share with Lilly Phase 1B and 2 development costs with 75% of those costs borne by Lilly and 25% of the costs borne by us, (iv) will have the option to contribute funding to Phase 3 development on an indication-by-indication basis ranging from zero to 25% of development costs, and (v) will have the opportunity to receive a royalty rate up to the low twenties based upon our Phase 3 development cost contribution and the level of annual global product sales. Lilly will be responsible for all costs of global commercialization, and we will have an option to co-promote in the U.S. under certain conditions. A portion of the development milestones may be reduced by 50% under certain conditions, related to the final formulation of the approved product and the timing of prior approval (if any) of competitive products with a similar mechanism of action, which could reduce these milestone payments by 75% if both conditions occur.

The agreement will continue until Lilly no longer has any royalty payment obligations or, if earlier, the termination of the agreement in accordance with its terms. The agreement may be terminated by Lilly for convenience, and may also be terminated under certain other circumstances, including material breach.

We identified our license grant to Lilly, our Phase 1 clinical development obligation and our drug product development obligation as the significant performance obligations in the arrangement. The valuation of each performance obligation involves significant estimates and assumptions, including but not limited to, expected market opportunity and pricing, assumed royalty rates, clinical trial costs, timelines and likelihood of success; in each case these estimates and assumptions covering long time periods. We determined the selling price for the license based on a discounted cash flow analysis of projected revenues from NKTR-358 and development and commercial costs using a discount rate based on a market participant’s weighted-average cost of capital adjusted for forecasting risk. We determined the selling prices for our Phase 1 clinical development and drug product development deliverables based on the nature of the services to be performed and estimates of the associated efforts and third-party rates for similar services.

Although we are entitled to significant development milestones under this arrangement, through December 31, 2020, we have excluded such milestones from the transaction price due to the significant uncertainties involved with clinical development. We have therefore determined the transaction price to consist of the upfront payment of $150.0 million received in September 2017. Based on our estimates of the standalone selling prices of the performance obligations, we allocated the $150.0 million upfront payment as $125.9 million to the license, $17.6 million to our portion of the Phase 1 clinical development and $6.5 million to the drug product development.

We recognized the $125.9 million of revenue allocated to the license upon the effective date of the license agreement in August 2017, since we determined that the license was a right to use our intellectual property, for which, as of the effective date, we had provided all necessary information to Lilly to benefit from the license and the license term had begun. We recognized revenue for our portion of the Phase 1 clinical development and drug product development using an input method, using costs incurred, as this method depicts our progress towards providing Lilly with the results of clinical trials and drug production processes. As of December 31, 2020, we have no deferred revenue related to this agreement.

Baxalta Incorporated/Takeda: Hemophilia

We are a party to an exclusive research, development, license and manufacturing and supply agreement with Baxalta Inc. (Baxalta), a subsidiary of Takeda Pharmaceutical Company Ltd. (Takeda), entered into in September 2005 to develop products designed to improve therapies for Hemophilia A patients using our PEGylation technology. Under the terms of the agreement, we are entitled to research and development funding for our active programs, which are now complete for Factor VIII, and are responsible for supplying Takeda with its requirements for our proprietary materials. Takeda is responsible for all

clinical development, regulatory, and commercialization expenses. The agreement is terminable by the parties under customary conditions.

This Hemophilia A program includes ADYNOVATE®, which was approved by the FDA in November 2015 for use in adults and adolescents, aged 12 years and older, who have Hemophilia A, and is now marketed in the U.S., the European Union, and many other countries. As a result of the marketing authorization in the EU in January 2018, we earned a $10.0 million development milestone, which we received in March 2018. During 2018, we earned an additional $10.0 million milestone for annual sales of ADYNOVATE®/ ADYNOVI™ reaching a certain specified amount. In addition, we are entitled to an additional sales milestone upon achievement of an annual worldwide net sales target and royalties based on worldwide net sales of products resulting from this agreement.

In October 2017, we entered into a right to sublicense agreement with Baxalta, under which we granted to Baxalta the right to grant a nonexclusive sublicense to certain patents that were previously exclusively licensed to Baxalta under our 2005 agreement. Under the right to sublicense agreement, Baxalta paid us $12.0 million in November 2017 and agreed to pay us single digit royalty payments based upon net sales of the products covered under the sublicense throughout the term of the agreement.

Our remaining unsatisfied performance obligation consists of our ongoing supply of PEGylation materials at a price less than the standalone selling price of these materials. As of December 31, 2020, our deferred revenue related to this agreement is not significant.

Amgen, Inc.: Neulasta®

In October 2010, we amended and restated an existing supply and license agreement by entering into a supply, dedicated suite and manufacturing guarantee agreement (the 2010 Agreement) and a license agreement with Amgen, Inc. and Amgen Manufacturing, Limited (together referred to as Amgen). Under the terms of the 2010 Agreement, we received a $50.0 million payment in the fourth quarter of 2010 in return for our guaranteeing the supply of certain quantities of our proprietary PEGylation materials to Amgen.

We determined that our obligation to manufacture and supply PEGylation materials and to maintain the dedicated manufacturing suite solely for the production of such materials for Amgen under the 2010 Agreement represented an obligation to stand ready to manufacture such materials. We concluded that we should recognize revenue based on the passage of time as this method depicts the satisfaction of Amgen’s right to require production of PEGylation materials at any time. We recognized revenue through October 2020, the month when the 2010 Agreement expired according to its terms. Accordingly, as of December 31, 2020, we have no deferred revenue related to our agreement with Amgen.

AstraZeneca AB: MOVANTIK® (naloxegol oxalate), previously referred to as naloxegol and NKTR-118,

In September 2009, we entered into an agreement with AstraZeneca AB (AstraZeneca) under which we granted AstraZeneca a worldwide, exclusive license under our patents and other intellectual property to develop, market, and sell MOVANTIK®. AstraZeneca is responsible for all research, development and commercialization costs and related decisions for MOVANTIK®. In September 2014 and December 2014, MOVANTIK® /MOVENTIG® was approved in the US and EU, respectively. As of December 31, 2020, we have received a total of $385.0 million of upfront and contingent milestone payments from this agreement, all of which was received in or before 2015. In addition, we are entitled to significant and escalating double-digit royalty payments and sales milestone payments based on annual worldwide net sales of MOVANTIK®.

In March 2016, AstraZeneca announced that it had entered into an agreement with ProStrakan Group plc, a subsidiary of Kyowa Hakko Kirin Co. Ltd. (Kirin), granting Kirin exclusive marketing rights to MOVENTIG® in the EU, Iceland, Liechtenstein, Norway and Switzerland. Under our license agreement with AstraZeneca, we and AstraZeneca share the upfront payment, market access milestone payments, royalties and sales milestone payments made by Kirin to AstraZeneca with AstraZeneca receiving 60% and Nektar receiving 40%. As of December 31, 2020, we have received a total of $37.6 million of milestone payments resulting from these sublicense arrangements, all of which was received in or before 2017.

As of December 31, 2020, we do not have deferred revenue related to our agreement with AstraZeneca.

As part of its approval of MOVANTIK®, the FDA required AstraZeneca to perform a post-marketing, observational epidemiological study comparing MOVANTIK® to other treatments of OIC in patients with chronic, non-cancer pain. As a result, the royalty rate payable to us from net sales of MOVANTIK® in the U.S. by AstraZeneca can be reduced by up to two percentage points to fund 33% of the external costs incurred by AstraZeneca to fund such post approval study, subject to a

$35.0 million aggregate cap. As a result of the 2020 Purchase and Sale Agreement as described in Note 7, AstraZeneca will deduct these costs from the royalties paid to HCR. Before we entered into the 2020 Purchase and Sale Agreement, our cumulative share of the post-approval study expenses was not significant. Any costs incurred by AstraZeneca can only be recovered by the reduction of the royalty payments. In no case can amounts be recovered by the reduction of a contingent payment due from AstraZeneca to us or through a payment from us to AstraZeneca.

In April 2020, AstraZeneca announced that it had sublicensed its global commercialization rights for MOVANTIK®, excluding Europe, Canada and Israel, to RedHill Biopharma. This sublicense does not change our rights under the agreement with AstraZeneca and our royalty rate, royalty term and future potential sales milestones remain unchanged.

Other

In addition, as of December 31, 2020, we have other collaboration agreements, including with our collaboration partner UCB Pharma, under which we are entitled to up to a total of $40.0 million of development milestone payments upon achievement of certain development objectives, as well as sales milestones upon achievement of annual sales targets and royalties based on net sales of commercialized products, if any. However, given the current phase of development of the potential products under these collaboration agreements, we cannot estimate the probability or timing of achieving these milestones and, therefore, have excluded all development milestones from the respective transaction prices for these agreements. As of December 31, 2020, we have deferred revenue of approximately $2.0 million related to these other collaboration agreements.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Stock-Based Compensation

We recognize total stock-based compensation expense in our Consolidated Statements of Operations as follows (in thousands):


	Year Ended December 31,
	2020		2019		2018
Cost of goods sold	$	2,825	$	4,294	$	4,629
Research and development	57,116		63,224		56,193
General and administrative	33,295		32,277		27,279
Impairment of assets and other costs for terminated program	1,025		—		—
Total stock-based compensation	$	94,261	$	99,795	$	88,101

The stock-based compensation expense reported in impairment of assets and other costs for terminated program results from executive severance.

As of December 31, 2020, total unrecognized compensation costs of $193.7 million related to unvested stock-based compensation arrangements are expected to be recognized as expense over a weighted-average period of 1.79 years.

Stock-based compensation expense resulting from PSUs and our ESPP was not significant in the years ended December 31, 2020, 2019, and 2018.

Black-Scholes Assumptions

The following table lists the Black-Scholes option-pricing model assumptions used to calculate the fair value of employee and director stock options, as well as the resulting grant-date fair value:


	Year Ended December 31,
	2020			2019			2018
Average risk-free interest rate	0.4		%	1.8		%	2.8		%
Dividend yield	0.0		%	0.0		%	0.0		%
Average volatility factor	64.1		%	62.2		%	61.0		%
Weighted-average expected life	5.6 years			5.6 years			5.1 years
Weighted-average grant-date fair value of options granted	$	10.70		$	12.25		$	29.86

The average risk-free interest rate is based on the U.S. treasury yield curve in effect at the time of grant for periods commensurate with the expected life of the stock-based award. We have never paid dividends, nor do we expect to pay dividends in the foreseeable future; therefore, we used a dividend yield of zero. Our estimate of expected volatility is based on

the daily historical trading data of our common stock at the time of grant over a historical period commensurate with the expected life of the stock-based award. We estimated the weighted-average expected life based on the contractual and vesting terms of the stock options, as well as historical cancellation and exercise data.

Summary of Stock Option Activity

The table below presents a summary of stock option activity under our equity incentive plans (in thousands, except for price per share and contractual life information):


	Number of Shares	Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Life (in Years)	Aggregate Intrinsic Value(1)
Outstanding at December 31, 2019	14,885	$	25.23
Options granted	1,654	19.15
Options exercised	(1,669)	11.69
Options forfeited & canceled	(1,233)	45.70
Outstanding at December 31, 2020	13,637	$	24.30	3.96	$	23,478

Exercisable at December 31, 2020	9,523	22.99		2.71	$	23,468

_______________________________________________________________

(1)Aggregate intrinsic value represents the difference between the exercise price of the option and the closing market price of our common stock on December 31, 2020.

The intrinsic value of options exercised during the years ended December 31, 2020, 2019 and 2018 totaled $15.9 million, $30.6 million and $303.4 million, respectively.

Summary of RSU Activity

A summary of RSU award activity is as follows (in thousands except for per share amounts):


	Units Issued	Weighted- Average Grant Date Fair Value
Balance at December 31, 2019	4,935	$	30.85
Granted	4,686	19.24
Vested and released	(1,661)	34.83
Forfeited and canceled	(866)	29.66
Balance at December 31, 2020	7,094	$	22.46

The fair value of restricted stock that vested in the years ended December 31, 2020, 2019 and 2018 totaled $33.3 million, $32.4 million and $80.4 million, respectively.

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

Income (loss) before provision for income taxes includes the following components (in thousands):


	Year Ended December 31,
	2020		2019		2018
Domestic	$	(445,370)	$	(441,494)	$	680,423
Foreign	1,423		1,440		2,302
Income (loss) before provision for income taxes	$	(443,947)	$	(440,054)	$	682,725

Provision for Income Taxes

The provision for income taxes consists of the following (in thousands):


	Year Ended December 31,
	2020		2019		2018
Current:
Federal	$	—	$	—	$	—
State	165		139		699
Foreign	364		495		620
Total Current	529		634		1,319
Deferred:
Federal	—		—		—
State	—		—		—
Foreign	(36)		(21)		93
Total Deferred	(36)		(21)		93
Provision for income taxes	$	493	$	613	$	1,412

Our income tax provision related to continuing operations differs from the amount computed by applying the statutory income tax rate of 21% for the years ended December 31, 2020, 2019 and 2018 to pretax income (loss) as follows (in thousands):


	Year Ended December 31,
	2020		2019		2018
Income tax expense (benefit) at federal statutory rate	$	(93,229)	$	(92,411)	$	143,372
Research credits	(3,081)		(10,511)		(17,295)
Premium on equity issuance	—		—		(12,551)
Change in valuation allowance	87,060		104,440		(46,885)
Stock-based compensation	7,929		(672)		(66,716)
Non-cash royalty revenue related to sale of future royalties	(7,967)		(7,624)		(6,995)
Non-cash interest expense on liability related to sale of future royalties	6,356		5,259		4,451
Other	3,425		2,132		4,031
Provision for income taxes	$	493	$	613	$	1,412

Deferred Tax Assets and Liabilities

Deferred income taxes reflect the net tax effects of loss and credit carryforwards and temporary differences between the carrying amount of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. We measure deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future. Significant components of our deferred tax assets for federal and state income taxes are as follows (in thousands):


	December 31,
	2020		2019
Deferred tax assets:
Net operating loss carryforwards	$	456,284	$	399,361
Research and other credits	132,994		128,015
Operating lease liabilities	35,672		36,907
Liability related to the sale of future royalties	32,737		—
Stock-based compensation	32,517		30,875
Other	11,688		13,568
Deferred tax assets before valuation allowance	701,892		608,726
Valuation allowance for deferred tax assets	(670,103)		(575,087)
Total deferred tax assets	31,789		33,639
Deferred tax liabilities:
Operating lease right-of-use assets	(29,707)		(31,718)
Other	(1,856)		(1,725)
Total deferred tax liabilities	(31,563)		(33,443)
Net deferred tax assets	$	226	$	196

Realization of our deferred tax assets is dependent upon future earnings, if any, the timing and amount of which are uncertain. Because of our lack of U.S. earnings history, other than income resulting from revenue recognized from the BMS Collaboration Agreement, and projected future losses, we have fully reserved our net U.S. deferred tax assets with a valuation allowance. The valuation allowance increased by $95.0 million and $114.6 million during the years ended December 31, 2020 and 2019, respectively, primarily due to the additional domestic net operating losses and credits generated in the current year that are not more likely than not of being utilized.

Net Operating Loss and Tax Credit Carryforwards

As of December 31, 2020, we had a net operating loss carryforward for federal income tax purposes of approximately $2.0 billion, portions of which will begin to expire in 2021. As of December 31, 2020, we had a total state net operating loss carryforward of approximately $1.3 billion, portions of which will begin to expire in 2026. Utilization of some of the federal and state net operating loss and credit carryforwards are subject to annual limitations due to the “change in ownership” provisions of the Internal Revenue Code of 1986 and similar state provisions.

We have federal research credits of approximately $98.9 million, which will begin to expire in 2023 and state research credits of approximately $44.0 million which have no expiration date. We have federal orphan drug credits of $17.7 million which will begin to expire in 2026. These tax credits are subject to the same limitations discussed above.

Unrecognized tax benefits

We have the following activity relating to unrecognized tax benefits (in thousands):


	Year Ended December 31,
	2020		2019		2018
Beginning balance	$	77,410	$	27,419	$	20,483
Tax positions related to current year:
Additions	2,512		49,858		5,664
Reductions	—		—		—
Tax positions related to prior years:
Additions	193		277		1,272
Reductions	(1,450)		(144)		—
Settlements	—		—		—
Lapses in statute of limitations	—		—		—
Ending balance	$	78,665	$	77,410	$	27,419

If we are eventually able to recognize our uncertain positions, our effective tax rate may be reduced. We currently have a full valuation allowance against our U.S. net deferred tax asset which would impact the timing of the effective tax rate benefit should any of these uncertain tax positions be favorably settled in the future. Adjustments to the substantial majority of our uncertain tax positions would result in an adjustment of our net operating loss or tax credit carry forwards rather than resulting in a cash outlay.

We file income tax returns in the U.S., California, Alabama, certain other states and India. Because of net operating losses and research credit carryovers, substantially all of our domestic tax years remain open and subject to examination. We may be subject to examination in India from time to time, but we do not believe that any resulting liability resulting from such an examination would have a material effect on our financial position or results of operations.

Our policy is to include interest and penalties related to unrecognized tax benefits, if any, within the provision for income taxes in the consolidated statements of operations. During the years ended December 31, 2020, 2019 and 2018, no significant interest or penalties were recognized relating to unrecognized tax benefits. Although it is reasonably possible that certain unrecognized tax benefits could change in the future, we do not anticipate any changes over the next twelve months.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Segment Reporting

12 Months Ended

Dec. 31, 2020

Segment Reporting [Abstract]

Segment Reporting

We operate in one business segment which focuses on applying our technology platforms to develop novel drug candidates. Our business offerings have similar economics and other characteristics, including the nature of products and manufacturing processes, types of customers, distribution methods and regulatory environment. We are comprehensively managed as one business segment by our Chief Executive Officer.

Our revenue is derived primarily from customers in the pharmaceutical and biotechnology industries. Revenue from BMS, UCB Pharma, Baxalta / Takeda, and AstraZeneca represented 33%, 23%, 14% and 13% of our revenue, respectively, for the year ended December 31, 2020. Revenue from UCB Pharma, Baxalta / Takeda, and AstraZeneca represented 28%, 19%, and 17% of our revenue for the year-ended December 31, 2019. Revenue from BMS represented 89% of our revenue, for the year ended December 31, 2018.

Revenue by geographic area is based on the headquarters or shipping locations of our partners. The following table sets forth revenue by geographic area (in thousands):


	Year Ended December 31,
	2020		2019		2018
United States	$	64,966	$	27,093	$	1,090,794
Rest of World	87,949		87,524		102,529
Total revenue	$	152,915	$	114,617	$	1,193,323

At December 31, 2020, $54.5 million, or approximately 91%, of the net book value of our property, plant and equipment was located in the United States and $5.1 million, or approximately 9%, was located in India. At December 31,

2019, $59.7 million, or approximately 92%, of the net book value of our property, plant and equipment was located in the United States and $5.3 million, or approximately 8%, was located in India.

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8924-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8981-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8721-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9031-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 26
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8844-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8657-108599

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8721-108599

Reference 14: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-URI http://asc.fasb.org/topic&trid=2134510

+ Details

Subsequent Event	12 Months Ended
Subsequent Event	Dec. 31, 2020
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event On February 12, 2021, we entered into a co-development agreement (the Agreement) with SFJ Pharmaceuticals XII, L.P., an SFJ Pharmaceuticals Group company (SFJ), pursuant to which SFJ will pay up to $150.0 million in committed funding to support a Phase 2/3 study of bempegaldesleukin in combination with Keytruda® for first-line treatment of patients with metastatic or unresectable recurrent squamous cell carcinoma of the head and neck (the SCCHN Clinical Trial) whose tumors express PD-L1 (the SCCHN Indication). SFJ Pharmaceuticals is a global drug development company backed by Blackstone Life Sciences and Abingworth. SFJ will have primary responsibility for the clinical trial management of the SCCHN Clinical Trial, and we will be the sponsor of the SCCHN Clinical Trial and will also have sole responsibility for regulatory interactions and approval activities for bempegaldesleukin. We and BMS, pursuant to the BMS Collaboration Agreement, remain solely responsible for conducting the Phase 3 clinical trials of bempegaldesleukin in combination with Opdivo®, including the treatment of previously untreated unresectable or metastatic melanoma (the “Melanoma Indication” and the “Melanoma Clinical Trial”). Other than the opportunity to receive Success Payments as outlined below, SFJ has no right to reimbursement of costs incurred by SFJ for the SCCHN Clinical Trial in the event that the Melanoma Clinical Trial and/or the SCCHN Clinical Trial do not meet their primary endpoints. We will pay SFJ a series of success-based annual payments (collectively, the Success Payments) in the event of FDA approval of bempegaldesleukin for the Melanoma Indication, the SCCHN Indication, or both, and in the event of FDA approval of one additional bempegaldesleukin indication. The Success Payments do not begin until the completion of certain SCCHN Clinical Trial activities. The total success-based annual payments for the first indication approved by FDA, whether for the Melanoma Indication or the SCCHN Indication, is an aggregate of $450.0 million, paid in annual installments over five years. The total success-based payments for the second indication approved by FDA, whether for the Melanoma Indication or the SCCHN Indication, is an aggregate of $150.0 million, paid in annual installments over seven years. Finally, in the event of FDA approval for bempegaldesleukin for any indication other than the Melanoma Indication or the SCCHN Indication, we will make a one-time payment of $37.5 million to SFJ. The Agreement provides for certain positive and negative covenants, including restrictions on our ability to incur liens on our intellectual property related to bempegaldesleukin (the bempegaldesleukin IP), or assign or convey any right to receive income with respect to the bempegaldesleukin IP (other than royalty and other license fee obligations to licensors), except for the issuance of senior secured debt secured by all or substantially all of our assets, including the bempegaldesleukin IP. The Agreement expires upon the payment of all Success Payments to SFJ, unless earlier terminated as provided under the Agreement. The Agreement may be terminated by either party for a safety or health concern for the patients, whether by the independent data monitoring company or by mutual agreement of both parties. The Agreement may also be terminated by either party for material breach or insolvency of the counterparty.

Selected Quarterly Financial Data

12 Months Ended

Dec. 31, 2020

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data

Selected Quarterly Financial Data (Unaudited)

The following table sets forth certain unaudited quarterly financial data. In our opinion, the unaudited information set forth below has been prepared on the same basis as our audited information and includes all adjustments necessary to present fairly the information set forth herein. We have experienced fluctuations in our quarterly results and expect these fluctuations to continue in the future. Due to these and other factors, we believe that quarter-to-quarter comparisons of our operating results will not be meaningful, and the results for any one quarter may not be indicative of our future performance. All data is in thousands except per share information.


	Year Ended December 31, 2020								Year Ended December 31, 2019
	Q1		Q2		Q3		Q4		Q1		Q2		Q3		Q4
Product sales	$	3,444	$	5,485	$	5,691	$	2,884	$	4,398	$	4,346	$	5,558	$	5,815
Total revenue	$	50,573	$	48,847	$	30,033	$	23,462	$	28,222	$	23,315	$	29,218	$	33,862
Cost of goods sold	$	3,811	$	5,773	$	5,570	$	4,323	$	5,440	$	5,018	$	4,927	$	5,989
Research and development expenses	$	108,987	$	96,436	$	100,531	$	102,724	$	118,463	$	106,686	$	99,048	$	110,369
Operating loss	$	(133,631)	$	(77,709)	$	(103,050)	$	(110,721)	$	(120,687)	$	(110,970)	$	(98,740)	$	(109,638)
Net loss	$	(138,651)	$	(80,000)	$	(108,586)	$	(117,203)	$	(119,632)	$	(110,286)	$	(98,585)	$	(112,164)
Net loss per share(1)
Basic	$	(0.78)	$	(0.45)	$	(0.61)	$	(0.65)	$	(0.69)	$	(0.63)	$	(0.56)	$	(0.64)
Diluted	$	(0.78)	$	(0.45)	$	(0.61)	$	(0.65)	$	(0.69)	$	(0.63)	$	(0.56)	$	(0.64)

_______________________________________________________________

(1)Quarterly income (loss) per share amounts may not total to the year-to-date income (loss) per share due to rounding.

Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization We are a research-based biopharmaceutical company headquartered in San Francisco, California and incorporated in Delaware. We are developing a pipeline of drug candidates that utilize our advanced polymer conjugate technology platforms, which are designed to enable the development of new molecular entities that target known mechanisms of action. Our research and development pipeline of new investigational drugs includes investigational treatments for cancer, autoimmune disease and viral infections. Our research and development activities have required significant ongoing investment to date and are expected to continue to require significant investment. As a result, we expect to continue to incur substantial losses and negative cash flows from operations in the future. We have financed our operations primarily through cash generated from licensing, collaboration and manufacturing agreements and financing transactions.
Basis of Presentation, Principles of Consolidation and Use of Estimates	Basis of Presentation, Principles of Consolidation and Use of Estimates Our Consolidated Financial statements include the financial position, results of operations and cash flows of our wholly-owned subsidiaries: Inheris Biopharma, Inc. (Inheris), Nektar Therapeutics (India) Private Limited (Nektar India) and Nektar Therapeutics UK Limited. We have eliminated all intercompany accounts and transactions in consolidation. Our Consolidated Financial Statements are denominated in U.S. dollars. Accordingly, changes in exchange rates between the applicable foreign currency and the U.S. dollar will affect the translation of each foreign subsidiary’s financial results into U.S. dollars for purposes of reporting our consolidated financial results. We include translation gains and losses in accumulated other comprehensive loss in the stockholders’ equity section of our Consolidated Balance Sheets. To date, such cumulative currency translation adjustments have not been significant to our consolidated financial position. Our comprehensive income (loss) consists of our net income (loss) plus our foreign currency translation gains and losses and unrealized holding gains and losses on available-for-sale securities. There were no significant reclassifications out of accumulated other comprehensive loss to the statements of operations during the years ended December 31, 2020, 2019 and 2018. The preparation of consolidated financial statements in conformity with U.S. generally accepted accounting principles (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Accounting estimates and assumptions are inherently uncertain. Actual results could differ materially from those estimates and assumptions. Our estimates include those related to the selling prices of performance obligations and amounts of variable consideration in collaboration agreements, royalty revenue, and other assumptions required for revenue recognition as described further below; the net realizable value of inventory; the impairment of investments, goodwill and long-lived assets; contingencies, accrued clinical trial, contract manufacturing and other expenses; non-cash royalty revenue and non-cash interest expense from our liabilities related to our sales of future royalties; assumptions used in stock-based compensation; and ongoing litigation, among other estimates. We base our estimates on historical experience and on other assumptions that management believes are reasonable under the circumstances. These estimates form the basis for making judgments about the carrying values of assets and liabilities when these values are not readily apparent from other sources. As appropriate, we assess estimates each period, update them to reflect current information, and will generally reflect any changes in estimates in the period first identified.
Reclassifications	Reclassifications Certain items previously reported in specific financial statement captions have been reclassified to conform to the current period presentation. Such reclassifications do not materially impact previously reported revenue, operating loss, net loss, total assets, liabilities or stockholders’ equity.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The recorded amounts of certain financial instruments, including cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities. Investments that are classified as available-for-sale are recorded at estimated fair value. The disclosed fair value related to our cash equivalents and investments is based on market prices from a variety of industry standard data providers and generally represent quoted prices for similar assets in active markets or have been derived from observable market data.
Cash, Cash Equivalents, and Investments in Marketable Securities	Cash, Cash Equivalents, and Investments in Marketable Securities We consider all investments in marketable securities with an original maturity of three months or less when purchased to be cash equivalents. We classify investments in securities with remaining maturities of less than one year, or where our intent is to use the investments to fund current operations or to make them available for current operations, as short-term investments. We classify investments in securities with remaining maturities of over one year as long-term investments. Investments are designated as available-for-sale and are carried at fair value with unrealized gains and losses reported in stockholders’ equity as accumulated other comprehensive income loss. We review our portfolio of available-for-sale debt securities, using both quantitative and qualitative factors, to determine if declines in fair value below amortized cost have resulted from a credit-related loss or other factors. If the decline in fair value is due to credit-related factors, we recognize a loss in our Consolidated Statement of Operations, whereas if the decline in fair value is not due to credit-related factors, we recognize the loss in other comprehensive income (loss). We include coupon interest on securities classified as available-for-sale, as well as amortization of premiums and accretion of discounts to maturity, in interest income. The cost of securities sold is based on the specific identification method. Our cash, cash equivalents, short-term investments and long-term investments are exposed to credit risk in the event of default by the third parties that hold or issue such assets. Our cash, cash equivalents, short-term investments and long-term investments are held or issued by financial institutions that management believes are of high credit quality. Our investment policy limits investments to fixed income securities denominated and payable in U.S. dollars such as corporate bonds, corporate commercial paper, U.S. government obligations, and money market funds and places restrictions on maturities and concentrations by type and issuer. For our available-for-sale securities, we have significant concentrations of issuers in the banking and financial services industry. While our investment policy requires that we only invest in highly-rated securities and limit our exposure to any single issuer, the COVID-19 pandemic may materially affect the financial condition of issuers. Additionally, pursuant to our investment policy, we may sell securities before maturity if the issuer’s credit rating has been downgraded below our minimum credit rating requirements, which may result in a loss on the sale. As a result of the COVID-19 pandemic, we have seen credit downgrades for certain of our securities. Accordingly, if the COVID-19 pandemic or other factors result in downgrades below our minimum credit rating requirements and if we decide to sell these securities, we may experience losses on such sales.
Accounts Receivable and Significant Customer Concentrations	Accounts Receivable and Significant Customer Concentrations Our customers are primarily pharmaceutical and biotechnology companies that are primarily located in the U.S. and Europe and with whom we have multi-year arrangements. Our accounts receivable balance contains billed and unbilled trade receivables from product sales, milestones (to the extent that they have been achieved and are due from the counterparty), other contingent payments and royalties, as well as reimbursable costs from collaborative research and development agreements. For the year ended December 31, 2020, our accounts receivable included $38.7 million for unbilled net expense reimbursements from our collaboration partner Bristol-Myers Squibb Company (BMS) and $0.2 million under customer contracts from our collaboration partners. For the year ended December 31, 2019, our accounts receivable included $24.0 million for unbilled net expense reimbursements from BMS and $12.8 million from customer contracts, which included our estimate of $11.6 million for royalties resulting from net sales of MOVANTIK®, ADYNOVATE® and REBINYN® during the three months ended December 31, 2019. Since we sold our rights to receive royalties in the 2020 Purchase and Sale Agreement with Healthcare Royalty Management, LLC, as discussed further in Note 7, we did not record accounts receivable for these royalties at December 31, 2020. We generally do not require collateral from our partners. We perform a regular review of our partners’ credit risk and payment histories when circumstances warrant, including payments made subsequent to year-end. When appropriate, we provide for an allowance for doubtful accounts by reserving for specifically identified doubtful accounts, although historically we have not experienced credit losses from our accounts receivable. At December 31, 2019, three different partners represented 65%, 17% and 14%, respectively, of our accounts receivable.
Inventory and Significant Supplier Concentrations	Inventory and Significant Supplier Concentrations We generally manufacture inventory upon receipt of firm purchase orders from our collaboration partners, and we may manufacture certain intermediate work-in-process materials and purchase raw materials based on purchase forecasts from our collaboration partners. Inventory includes direct materials, direct labor, and manufacturing overhead, and we determine cost on a first-in, first-out basis for raw materials and on a specific identification basis for work-in-process and finished goods. We value inventory at the lower of cost or net realizable value, and we write down defective or excess inventory to net realizable value based on historical experience or projected usage. We expense inventory related to our research and development activities when we purchase or manufacture it. Before the regulatory approval of our drug candidates, we recognize research and development expense for the manufacture of drug products that could potentially be available to support the commercial launch of our drug candidates, if approved. We are dependent on our suppliers and contract manufacturers to provide raw materials and drugs of appropriate quality and reliability and to meet applicable contract and regulatory requirements. In certain cases, we rely on single sources of supply of one or more critical materials. Consequently, in the event that supplies are delayed or interrupted for any reason, including as a result of the COVID-19 pandemic, our ability to develop and produce our drug candidates, our ability to supply comparator drugs for our clinical trials, or our ability to meet our supply obligations could be significantly impaired, which could have a material adverse effect on our business, financial condition and results of operations.
Leases	Leases On January 1, 2019, we adopted Accounting Standards Codification (ASC) 842, Leases (ASC 842). ASC 842 supersedes the guidance in ASC 840, Leases (ASC 840). Under ASC 842, an entity recognizes a right-of-use asset and a corresponding lease liability, measured as the present value of the lease payments. In our adoption, we used the package of practical expedients, which, among other things, allowed us to carry forward our historical lease classification of those leases in effect as of January 1, 2019. We present results for the year ended December 31, 2020 and 2019 under ASC 842. We have not restated the results for the year ended December 31, 2018 continue to report them under ASC 840. We determine if an arrangement contains a lease at the inception of the arrangement. Right-of-use assets represent our right to use an underlying asset for the lease term, and lease liabilities represent our obligation to make lease payments arising from the lease. We recognize operating lease right-of-use assets and liabilities at the lease commencement date based on the present value of lease payments over the expected lease term. In determining the present value of lease payments, we use our incremental borrowing rate based on the information available at the lease commencement date. However, in determining the present value of our lease payments for leases in effect when we adopted ASC 842, we used our incremental borrowing rate as of January 1, 2019. We have elected the practical expedient to account for the lease and non-lease components, such as common area maintenance charges, as a single lease component for our facilities leases, and elected the short-term lease recognition exemption for our short-term leases, which allows us not to recognize lease liabilities and right-of-use assets for leases with an original term of twelve months or less. Our expected lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise any such options. We recognize lease expense for our operating leases on a straight-line basis over the expected lease term. We have elected to recognize lease incentives, such as tenant improvement allowances, at the lease commencement date as a reduction of the right-of-use asset and lease liability until paid to us by the lessor to the extent that the lease provides a specified fixed or maximum level of reimbursement and we are reasonably certain to incur reimbursable costs at least equaling such amounts. For leases in effect as of January 1, 2019, we recognized our lease incentives as part of our transition adjustment. Please see Note 6 for additional information regarding our leases.
Long-Lived Assets	Long-Lived Assets We state property, plant and equipment at cost, net of accumulated depreciation. We capitalize major improvements and expense maintenance and repairs as incurred. We generally recognize depreciation on a straight-line basis. We depreciate manufacturing, laboratory and other equipment over their estimated useful lives of generally three to ten years, depreciate buildings over the estimated useful life of generally twenty years and amortize leasehold improvements over the shorter of the estimated useful lives or the remaining term of the related lease. Goodwill represents the excess of the price paid for another entity over the fair value of the assets acquired and liabilities assumed in a business combination. We are organized in one reporting unit and evaluate the goodwill for the Company as a whole. Goodwill has an indefinite useful life and is not amortized, but instead tested for impairment at least annually in the fourth quarter of each year using an October 1 measurement date. We assess the impairment of long-lived assets whenever events or changes in business circumstances indicate that the carrying amounts of the assets may not be fully recoverable. In the case of property, plant and equipment and right-of-use assets for our leases, we determine whether there has been an impairment by comparing the carrying value of the asset to the anticipated undiscounted net cash flows associated with the asset. If such cash flows are less than the carrying value, we write down the asset to its fair value, which may be measured as anticipated discounted net cash flows associated with the asset. In the case of goodwill impairment, we compare the carrying value of the reporting unit to its fair value, which we generally measure using market capitalization for our single reporting unit. If an impairment exists, we write down goodwill such that the carrying value of the reporting units equals its fair value.
Collaborative Arrangements	Collaborative Arrangements We enter into collaboration arrangements with pharmaceutical and biotechnology collaboration partners, under which we may grant licenses to our collaboration partners to further develop and commercialize one of our proprietary drug candidates, either alone or in combination with the collaboration partners’ compounds, or grant licenses to partners to use our technology to research and develop their own proprietary drug candidates. We may also perform research, development, manufacturing and supply activities under our collaboration agreements. Consideration under these contracts may include an upfront payment, development and regulatory milestones and other contingent payments, expense reimbursements, royalties based on net sales of approved drugs, and commercial sales milestone payments. Additionally, these contracts may provide options for the customer to purchase our proprietary PEGylation materials, drug candidates or additional contract research and development services under separate contracts. When we enter into collaboration agreements, we assess whether the arrangements fall within the scope of ASC 808, Collaborative Arrangements (ASC 808) based on whether the arrangements involve joint operating activities and whether both parties have active participation in the arrangement and are exposed to significant risks and rewards of the arrangement. To the extent that the arrangement falls within the scope of ASC 808, we assess whether the payments between us and our collaboration partner fall within the scope of other accounting literature. If we conclude that payments from the collaboration partner to us represent consideration from a customer, such as license fees and contract research and development activities, we account for those payments within the scope of ASC 606, Revenue from Contracts with Customers (ASC 606). However, if we conclude that our collaboration partner is not a customer for certain activities and associated payments, such as for certain collaborative research, development, manufacturing and commercial activities, we present such payments as a reduction of research and development expense or general and administrative expense, based on where we present the underlying expense.
Revenue Recognition	Revenue Recognition For elements of those arrangements that we determine should be accounted for under ASC 606, we assess which activities in our collaboration agreements are performance obligations that should be accounted for separately and determine the transaction price of the arrangement, which includes the assessment of the probability of achievement of future milestones and other potential consideration. For arrangements that include multiple performance obligations, such as granting a license or performing contract research and development activities or participation on joint steering or other committees, we allocate upfront and milestone payments under a relative standalone selling price method. Accordingly, we develop assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. These key assumptions may include revenue forecasts, clinical development timelines and costs, discount rates and probabilities of clinical and regulatory success. Product sales Product sales are primarily derived from manufacturing and supply agreements with our customers. We have assessed our current manufacturing and supply arrangements and have generally determined that they provide the customer an option to purchase our proprietary PEGylation materials. Accordingly, we treat each purchase order as a discrete exercise of the customer’s option (i.e. a separate contract) rather than as a component of the overall arrangement. The pricing for the manufacturing and supply is generally at a fixed price and may be subject to annual producer price index (PPI) adjustments. We invoice and recognize product sales when title and risk of loss pass to the customer, which generally occurs upon shipment. Customer payments are generally due 30 days from receipt of invoice. We test our products for adherence to technical specifications before shipment; accordingly, we have not experienced any significant returns from our customers. Royalty revenue Generally, for our collaboration arrangements that include sales-based royalties, we have granted our collaboration partner a license to our intellectual property. Pursuant to these arrangements, our collaboration partners are typically obligated to pay a royalty that is based on the net sales of their approved drugs that are sold in the countries where we have intellectual property rights covering their drugs. As of December 30, 2020, we have sold our rights to receive sales-based royalties for CIMZIA®, MIRCERA®, MOVANTIK®, ADYNOVATE® and REBINYN® as further described in Note 7. For collaboration arrangements that include sales-based royalties, we have concluded that the license is the predominant item to which the royalties relate, which include commercial milestone payments based on the level of sales. Accordingly, we recognize royalty revenue, including for our non-cash royalties, when the underlying sales occur based on our best estimates of sales of the drugs. Our partners generally pay royalties or commercial milestones after the end of the calendar quarter in accordance with contractual terms. We present commercial milestone payments within license, collaboration and other revenue. License, collaboration and other revenue License Grants: For collaboration arrangements that include a grant of a license to our intellectual property, we consider whether the license grant is distinct from the other performance obligations included in the arrangement. Generally, we would conclude that the license is distinct if the customer is able to benefit from the license with the resources available to it. For licenses that are distinct, we recognize revenues from nonrefundable, upfront payments and other consideration allocated to the license when the license term has begun and we have provided all necessary information regarding the underlying intellectual property to the customer, which generally occurs at or near the inception of the arrangement. Milestone Payments: At the inception of the arrangement and at each reporting date thereafter, we assess whether we should include any milestone payments or other forms of variable consideration in the transaction price, based on whether a significant reversal of revenue previously recognized is not probable upon resolution of the uncertainty. Since milestone payments may become payable to us upon the initiation of a clinical study, filing for or receipt of regulatory approval or the first commercial sale of a product, we review the relevant facts and circumstances to determine when we should update the transaction price, which may occur before the triggering event. When we do update the transaction price for milestone payments, we allocate it on a relative standalone selling price basis and record revenue on a cumulative catch-up basis, which results in recognizing revenue for previously satisfied performance obligations in such period. If we update the transaction price before the triggering event, we recognize the increase in the transaction price as a contract asset. Our partners generally pay development milestones subsequent to achievement of the triggering event. Research and Development Services: For amounts allocated to our research and development obligations in a collaboration arrangement, we recognize revenue over time using a proportional performance model, representing the transfer of goods or services as we perform activities over the term of the agreement.
Shipping and Handling Costs	Shipping and Handling Costs We recognize costs related to shipping and handling of product to customers in cost of goods sold.
Research and Development Expense	Research and Development Expense Research and development costs are expensed as incurred and include salaries, benefits and other operating costs such as outside services, supplies and allocated overhead costs. We perform research and development for our proprietary drug candidates and technology development and for certain third parties under collaboration agreements. For our proprietary drug candidates and our internal technology development programs, we invest our own funds without reimbursement from a third party. Where we perform research and development activities under a joint development collaboration, such as our collaboration with BMS, we record the cost reimbursement from our partner as a reduction to research and development expense when reimbursement amounts are due to us under the agreement. We record an accrued expense for the estimated costs of our clinical trial activities performed by third parties. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows to our vendors. Payments under the contracts depend on factors such as the achievement of certain events, successful enrollment of patients, and completion of certain clinical trial activities. We generally accrue costs associated with the start-up and reporting phases of the clinical trials ratably over the estimated duration of the start-up and reporting phases. We generally accrue costs associated with the treatment phase of clinical trials based on the estimated activities performed by third parties. We may also accrue expenses based on the total estimated cost of the treatment phase on a per patient basis and expense the per patient cost ratably over the estimated patient treatment period based on patient enrollment in the trials. In specific circumstances, such as for certain time-based costs, we recognize clinical trial expenses using a methodology that we consider to be more reflective of the timing of costs incurred. We record an accrued expense for the estimated costs of our contract manufacturing activities performed by third parties. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows to our vendors. Payments under the contracts include upfront payments and milestone payments, which depend on factors such as the achievement of the completion of certain stages of the manufacturing process. For purposes of recognizing expense, we assess whether we consider the production process is sufficiently defined such that the resulting product can be considered the delivery of a good, as evidenced by predictive or contractually required yields in the production process or payment terms based on the actual yield, or the delivery of a service, where processes and yields are developing and less certain. If we consider the process to be the delivery of a good, we recognize expense when the drug product is delivered, or we otherwise bear risk of loss. If we consider the process to be the delivery of a service, we recognize expense based on our best estimates of the contract manufacturer’s progress towards completion of the stages in the contracts. We recognize and amortize upfront payments and accrue liabilities based on the specific terms of each arrangement. Certain arrangements may provide upfront payments for certain stages of the arrangement and milestone payments for the completion of certain stages, and, accordingly, we may record advance payments for services that have not been completed or goods not delivered and liabilities for stages where the contract manufacturer is entitled to a milestone payment. We capitalize advance payments for goods or services that will be used or rendered for future research and development activities and recognize expense as the related goods are delivered or services performed. We base our estimates on the best information available at the time. However, additional information may become available to us in the future which may allow us to make a more accurate estimate in future periods. In this event, we may be required to record adjustments to research and development expenses in future periods when the actual level of activity becomes more certain. We generally consider such increases or decreases in cost as changes in estimates and reflect them in research and development expenses in the period identified.
Impairment of Assets and Other Costs for Terminated Program	Impairment of Assets and Other Costs for Terminated Program On January 14, 2020, the joint FDA Anesthetic Drug Products Advisory Committee and Drug Safety and Risk Management Committee did not recommend approval of our NDA for NKTR-181. As a result, we withdrew our NDA and decided to make no further investments in this program. On February 26, 2020, the Audit Committee of our Board of Directors approved management’s plan for the wind-down of Inheris and the NKTR-181 program. As a result, in the three months ended March 31, 2020, we wrote off $19.7 million of advance payments to contract manufacturers for commercial batches of NKTR-181. We also incurred $25.5 million of additional costs, primarily for non-cancellable commitments to our contract manufacturers and certain severance costs. We present these costs in the Impairment of assets and other costs for terminated program line in our Consolidated Statement of Operations. We did not incur any substantial costs related to the wind-down of Inheris and the NKTR-181 program after March 31, 2020. As of December 31, 2020, we have substantially completed our wind-down and do not expect to incur additional costs.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation arrangements include grants of stock options, restricted stock units (RSUs) and performance stock units (PSUs) under our equity incentive plans, as well as shares issued under our Employee Stock Purchase Plan (ESPP), through which employees may purchase our common stock at a discount to the market price. We expense the grant date fair value of options, RSUs and PSUs on a straight-line basis over the requisite service periods in our Consolidated Statements of Operations and recognize forfeitures of options, RSUs and PSUs as they occur. For options and RSUs that vest upon the achievement of performance milestones, we estimate the vesting period based on our evaluation of the probability of achievement of each respective milestone and the related estimated date of achievement. We recognize stock-based compensation expense for purchases under the ESPP over the respective six-month purchase period. We report expense amounts in cost of goods sold, research and development expense, and general and administrative expense based on the function of the applicable employee. Stock-based compensation charges are non-cash charges and have no effect on our reported cash flows. We estimate the grant date fair value of our stock-based compensation awards as follows: •We use the Black-Scholes option pricing model for the respective grant to determine the estimated fair value of the option on the date of grant (grant date fair value) and the estimated fair value of common stock purchased under the ESPP. The Black-Scholes option pricing model requires the input of highly subjective assumptions, including but not limited to, our stock price volatility over the term of the awards, and actual and projected employee stock option exercise behaviors. Because our employee stock options have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models may not provide a reliable single measure of the fair value of our employee stock options or common stock purchased under the ESPP. •The number of shares issuable under PSUs is based on our total shareholder return as compared to other companies within the Nasdaq biotechnology index over the measurement period and may be capped based on our absolute total shareholder return over such period. We use the Monte Carlo simulation model to determine the estimated grant date fair value. The Monte Carlo simulation model incorporates assumptions such as the volatility of our stock, the volatility of the stock of other peer companies within the index, and the correlation of both our stock and our peer companies’ stock to the index. •The fair value of an RSU is equal to the closing price of our common stock on the grant date. Management will continue to assess the assumptions and methodologies used to calculate the estimated fair value of stock-based compensation. Circumstances may change and additional data may become available over time, which could result in changes to these assumptions and methodologies, and which could materially impact our fair value determination.
Net Income (Loss) Per Share	Net Income (Loss) Per Share For all periods presented in the Consolidated Statements of Operations, the net income (loss) available to common stockholders is equal to the reported net income (loss). We calculate basic net income (loss) per share based on the weighted-average number of common shares outstanding during the periods presented and calculate diluted net income (loss) per share based on the weighted-average number of shares of common stock outstanding, including potentially dilutive securities, which consist of common shares underlying stock options and RSUs. For the years ended December 31, 2020 and 2019, basic and diluted net loss per share are the same due to our net losses and the requirement to exclude potentially dilutive securities which would have an antidilutive effect on net loss per share. We excluded weighted average outstanding stock options and RSUs totaling 17.4 million and 17.9 million for the years ended December 31, 2020 and 2019, respectively. For the year ended December 31, 2018, the effect of these dilutive securities under the treasury stock method was approximately 10.5 million, and we excluded approximately 3.3 million of weighted-average shares of common stock underlying outstanding stock options from the computation of diluted net income per share because their effect was antidilutive.
Income Taxes	Income Taxes We account for income taxes under the liability method. Under this method, we determine deferred tax assets and liabilities based on differences between the financial reporting and tax reporting bases of assets and liabilities, measured using enacted tax rates and laws that we expect to be in effect when we expect the differences to reverse. Realization of deferred tax assets is dependent upon future earnings, the timing and amount of which are uncertain. We record a valuation allowance against deferred tax assets to reduce their carrying value to an amount that is more likely than not to be realized. When we establish or reduce the valuation allowance related to the deferred tax assets, our provision for income taxes will increase or decrease, respectively, in the period we make such determination. We utilize a two-step approach to recognize and measure uncertain tax positions. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates that it is more likely than not that the position will be sustained upon tax authority examination, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount of benefit, determined on a cumulative probability basis, that is more than 50% likely of being realized upon ultimate settlement.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) is the change in stockholders’ equity from transactions and other events and circumstances other than those resulting from investments by stockholders and distributions to stockholders. Our other comprehensive income (loss) includes net income (loss), gains and losses from the foreign currency translation of the assets and liabilities of our India and UK subsidiaries, and unrealized gains and losses on investments in available-for-sale securities.
Coronavirus Aid, Relief and Economic Security (CARES) Act	Coronavirus Aid, Relief, and Economic Security (CARES) Act In March 2020, the U.S. government enacted the CARES Act, which includes modifications to the limitation on business interest expense and net operating loss provisions and provides a payment delay of employer payroll taxes during 2020 after the date of enactment. The CARES Act has not had a material effect on our results of operations or financial position.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements On January 1, 2020, we adopted Accounting Standards Update 2018-18: Clarifying the Interaction between Topic 808 and Topic 606 (ASU 2018-18). The guidance clarifies that certain transactions between collaborative arrangement participants should be accounted for as revenue under ASC 606 when the collaborative arrangement participant is a customer for a promised good or service that is distinct within the collaborative arrangement. The guidance also precludes entities from presenting amounts related to transactions with a collaborative arrangement participant that is not a customer as revenue, unless those transactions are directly related to third-party sales. ASU 2018-18 is applied retrospectively to January 1, 2018, when we adopted ASC 606. Our adoption of ASU 2018-18 did not materially affect our revenue recognition. On January 1, 2020, we adopted ASU 2016-13: Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The guidance modifies the measurement and recognition of credit losses for most financial assets and certain other instruments. The amendment updates the guidance for measuring and recording credit losses on financial assets measured at amortized cost by replacing the “incurred loss” model with an “expected loss” model. As a result of adoption, we present these financial assets, which include our accounts receivable and available-for-sale debt securities, at the net amount we expect to collect. The amendment also requires that we record credit losses related to available-for-sale debt securities as an allowance through net income rather than reducing the carrying amount under the historical, other-than-temporary-impairment model. Our adoption of ASU 2016-13 did not materially affect our Consolidated Financial Statements. Recent Accounting Pronouncements We have reviewed other recent accounting pronouncements and concluded they are either not applicable to us or that we do not expect adoption to have a material effect on our consolidated financial statements.

Cash and Investments in Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2020

Cash and Cash Equivalents [Abstract]

Cash and Investments in Marketable Securities, Including Cash Equivalents

Cash and investments in marketable securities, including cash equivalents, are as follows (in thousands):


	Estimated Fair Value at
	December 31, 2020		December 31, 2019
Cash and cash equivalents	$	198,955	$	96,363
Short-term investments	862,941		1,228,499
Long-term investments	136,662		279,119
Total cash and investments in marketable securities	$	1,198,558	$	1,603,981

Portfolio of Cash and Investments in Marketable Securities

Our portfolio of cash and investments in marketable securities includes (in thousands):


	Fair Value Hierarchy Level	December 31, 2020								December 31, 2019
		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value		Fair Value
Corporate notes and bonds	2	$	686,543	$	1,035	$	(109)	$	687,469	$	1,132,182
Corporate commercial paper	2	313,520		44		(67)		313,497		375,473
Obligations of U.S. government agencies	2	2,380		2		—		2,382		—
Available-for-sale investments		1,002,443		1,081		(176)		1,003,348		1,507,655
Money market funds	1							179,302		83,546
Certificate of deposit	N/A							9,623		6,951
Cash	N/A							6,285		5,829
Total cash and investments in marketable securities								$	1,198,558	$	1,603,981

Inventory (Tables)

12 Months Ended

Dec. 31, 2020

Inventory Disclosure [Abstract]

Inventory

Inventory consists of the following (in thousands):


	December 31,
	2020		2019
Raw materials	$	2,422	$	1,673
Work-in-process	10,703		8,267
Finished goods	2,167		2,725
Total inventory	$	15,292	$	12,665

Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2020

Property, Plant and Equipment [Abstract]

Property, Plant and Equipment

Property, plant and equipment consists of the following (in thousands):


	December 31,
	2020		2019
Building and leasehold improvements	$	92,977	$	93,097
Laboratory equipment	40,121		36,623
Computer equipment and software	28,684		26,910
Manufacturing equipment	21,796		22,030
Furniture, fixtures, and other	9,872		9,662
Depreciable property, plant and equipment at cost	193,450		188,322
Less: accumulated depreciation	(138,488)		(127,875)
Depreciable property, plant and equipment, net	54,962		60,447
Construction-in-progress	4,700		5,218
Property, plant and equipment, net	$	59,662	$	65,665

Leases (Tables)

12 Months Ended

Dec. 31, 2020

Leases [Abstract]

Schedule of Operating Lease Information

The following table presents key information regarding these leases (dollars in thousands):


	Mission Bay Facility		Third Street Facility
Lease commencement	September 2017		June 2018
Lease term	January 2030		January 2030
Space delivered during the year ended December 31, 2019
Square footage	13,907		67,105
Right-of-use asset and lease liability recognized	$	6,698	$	50,993
Space delivered during the year ended December 31, 2020
Square footage	4,940		—
Right-of-use asset and lease liability recognized	$	2,133	$	—
Renewal terms	Two consecutive five-year terms		One five-year term

Lease, Cost

The components of lease costs, which we include in operating expenses in our Consolidated Statements of Operations, were as follows (in thousands):


	Year Ended December 31,
	2020		2019		2018
Operating lease cost	$	18,985	$	14,697	$	7,972
Variable lease cost	8,179		6,408		4,497
Total lease costs	$	27,164	$	21,105	$	12,469

Future Minimum Lease Payments for Operating Leases

As of December 31, 2020, the maturities of our operating lease liabilities were as follows (in thousands):


Year ending December 31,
2021	$	17,938
2022	20,141
2023	20,780
2024	21,439
2025	22,117
2026 and thereafter	97,764
Total lease payments	200,179
Less: portion representing interest	(46,380)
Less: lease incentives	(3,511)
Operating lease liabilities	150,288
Less: current portion	(13,915)
Operating lease liabilities, less current portion	$	136,373

Liabilities Related to the Sales of Future Royalties (Tables)

12 Months Ended

Dec. 31, 2020

Summary of Liability Related to Potential Future Royalties


	Year-Ended December 31, 2020						Period from inception to December 31, 2020
	2012 Purchase and Sale Agreement		2020 Purchase and Sale Agreement		Total		2012 Purchase and Sale Agreement		2020 Purchase and Sale Agreement		Total
Liability related to the sale of future royalties—beginning balance	$	73,551	$	—	$	73,551	$	—	$	—	$	—
Royalty monetization proceeds	—		150,000		150,000		124,000		150,000		274,000
Non-cash royalty revenue	(37,938)		(10,625)		(48,563)		(245,080)		(10,625)		(255,705)
Non-cash interest expense	30,267		—		30,267		196,960		—		196,960
Payments to RPI	—		—		—		(10,000)		—		(10,000)
Liability related to the sale of future royalties – ending balance	65,880		139,375		205,255		65,880		139,375		205,255
Less: unamortized transaction costs	(1,165)		(3,750)		(4,915)		(1,165)		(3,750)		(4,915)
Liability related to the sale of future royalties, net	$	64,715	$	135,625	$	200,340	$	64,715	$	135,625	$	200,340


	2012 Purchase and Sale Agreement						2020 Purchase and Sale Agreement
	Year-Ended December 31,						Year-Ended December 31,
	2020		2019		2018		2020
Interest rates - end of period presented
Implicit interest rate over the life of the agreement	20.2	%	19.5	%	18.7	%	16.0	%
Prospective effective interest rate	48.0	%	38.0	%	29.0	%	16.0	%

License and Collaboration Agreements (Tables)

12 Months Ended

Dec. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

License, Collaboration and Other Revenue

In accordance with our collaboration agreements, we recognized license, collaboration and other revenue as follows (in thousands):


		Year Ended December 31,
Partner	Agreement	2020		2019		2018
Bristol-Myers Squibb	Bempegaldesleukin	$	50,000	$	—	$	1,059,768
Eli Lilly and Company	NKTR-358	1,259		7,019		11,634
Amgen, Inc.	Neulasta®	4,167		5,000		5,000
Baxalta Incorporated / Takeda	Hemophilia, including ADYNOVATE® and ADYNOVI®	346		378		20,328
Other		77		4,578		535
License, collaboration and other revenue		$	55,849	$	16,975	$	1,097,265

Changes in Deferred Revenue Balance from Collaboration Agreements

The following table presents the changes in our deferred revenue balance from our collaboration agreements during the year ended December 31, 2020 (in thousands):


	For the year ended December 31, 2020
Deferred revenue—December 31, 2019	$	8,071
Recognition of previously unearned revenue	(5,516)
Deferred revenue—December 31, 2020	$	2,555

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Stock-Based Compensation Expense

We recognize total stock-based compensation expense in our Consolidated Statements of Operations as follows (in thousands):


	Year Ended December 31,
	2020		2019		2018
Cost of goods sold	$	2,825	$	4,294	$	4,629
Research and development	57,116		63,224		56,193
General and administrative	33,295		32,277		27,279
Impairment of assets and other costs for terminated program	1,025		—		—
Total stock-based compensation	$	94,261	$	99,795	$	88,101

Black-Scholes Option-Pricing Model Assumptions Used to Calculate Fair Value of Employee Stock Options

The following table lists the Black-Scholes option-pricing model assumptions used to calculate the fair value of employee and director stock options, as well as the resulting grant-date fair value:


	Year Ended December 31,
	2020			2019			2018
Average risk-free interest rate	0.4		%	1.8		%	2.8		%
Dividend yield	0.0		%	0.0		%	0.0		%
Average volatility factor	64.1		%	62.2		%	61.0		%
Weighted-average expected life	5.6 years			5.6 years			5.1 years
Weighted-average grant-date fair value of options granted	$	10.70		$	12.25		$	29.86

Stock Option Activity Under Equity Incentive Plans

The table below presents a summary of stock option activity under our equity incentive plans (in thousands, except for price per share and contractual life information):


	Number of Shares	Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Life (in Years)	Aggregate Intrinsic Value(1)
Outstanding at December 31, 2019	14,885	$	25.23
Options granted	1,654	19.15
Options exercised	(1,669)	11.69
Options forfeited & canceled	(1,233)	45.70
Outstanding at December 31, 2020	13,637	$	24.30	3.96	$	23,478

Exercisable at December 31, 2020	9,523	22.99		2.71	$	23,468

_______________________________________________________________

(1)Aggregate intrinsic value represents the difference between the exercise price of the option and the closing market price of our common stock on December 31, 2020.

Restricted Stock Unit Award Activity

A summary of RSU award activity is as follows (in thousands except for per share amounts):


	Units Issued	Weighted- Average Grant Date Fair Value
Balance at December 31, 2019	4,935	$	30.85
Granted	4,686	19.24
Vested and released	(1,661)	34.83
Forfeited and canceled	(866)	29.66
Balance at December 31, 2020	7,094	$	22.46

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of Income before Income Tax, Domestic and Foreign

Income (loss) before provision for income taxes includes the following components (in thousands):


	Year Ended December 31,
	2020		2019		2018
Domestic	$	(445,370)	$	(441,494)	$	680,423
Foreign	1,423		1,440		2,302
Income (loss) before provision for income taxes	$	(443,947)	$	(440,054)	$	682,725

Provision for Income Taxes

The provision for income taxes consists of the following (in thousands):


	Year Ended December 31,
	2020		2019		2018
Current:
Federal	$	—	$	—	$	—
State	165		139		699
Foreign	364		495		620
Total Current	529		634		1,319
Deferred:
Federal	—		—		—
State	—		—		—
Foreign	(36)		(21)		93
Total Deferred	(36)		(21)		93
Provision for income taxes	$	493	$	613	$	1,412

Income Tax Provision Related to Continuing Operations


	Year Ended December 31,
	2020		2019		2018
Income tax expense (benefit) at federal statutory rate	$	(93,229)	$	(92,411)	$	143,372
Research credits	(3,081)		(10,511)		(17,295)
Premium on equity issuance	—		—		(12,551)
Change in valuation allowance	87,060		104,440		(46,885)
Stock-based compensation	7,929		(672)		(66,716)
Non-cash royalty revenue related to sale of future royalties	(7,967)		(7,624)		(6,995)
Non-cash interest expense on liability related to sale of future royalties	6,356		5,259		4,451
Other	3,425		2,132		4,031
Provision for income taxes	$	493	$	613	$	1,412

Significant Components of Deferred Tax Assets and Liabilities

We measure deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future. Significant components of our deferred tax assets for federal and state income taxes are as follows (in thousands):


	December 31,
	2020		2019
Deferred tax assets:
Net operating loss carryforwards	$	456,284	$	399,361
Research and other credits	132,994		128,015
Operating lease liabilities	35,672		36,907
Liability related to the sale of future royalties	32,737		—
Stock-based compensation	32,517		30,875
Other	11,688		13,568
Deferred tax assets before valuation allowance	701,892		608,726
Valuation allowance for deferred tax assets	(670,103)		(575,087)
Total deferred tax assets	31,789		33,639
Deferred tax liabilities:
Operating lease right-of-use assets	(29,707)		(31,718)
Other	(1,856)		(1,725)
Total deferred tax liabilities	(31,563)		(33,443)
Net deferred tax assets	$	226	$	196

Unrecognized Tax Benefits

We have the following activity relating to unrecognized tax benefits (in thousands):


	Year Ended December 31,
	2020		2019		2018
Beginning balance	$	77,410	$	27,419	$	20,483
Tax positions related to current year:
Additions	2,512		49,858		5,664
Reductions	—		—		—
Tax positions related to prior years:
Additions	193		277		1,272
Reductions	(1,450)		(144)		—
Settlements	—		—		—
Lapses in statute of limitations	—		—		—
Ending balance	$	78,665	$	77,410	$	27,419

Segment Reporting (Tables)

12 Months Ended

Dec. 31, 2020

Segment Reporting [Abstract]

Revenue by Geographic Area

The following table sets forth revenue by geographic area (in thousands):


	Year Ended December 31,
	2020		2019		2018
United States	$	64,966	$	27,093	$	1,090,794
Rest of World	87,949		87,524		102,529
Total revenue	$	152,915	$	114,617	$	1,193,323

Selected Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2020

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Data


	Year Ended December 31, 2020								Year Ended December 31, 2019
	Q1		Q2		Q3		Q4		Q1		Q2		Q3		Q4
Product sales	$	3,444	$	5,485	$	5,691	$	2,884	$	4,398	$	4,346	$	5,558	$	5,815
Total revenue	$	50,573	$	48,847	$	30,033	$	23,462	$	28,222	$	23,315	$	29,218	$	33,862
Cost of goods sold	$	3,811	$	5,773	$	5,570	$	4,323	$	5,440	$	5,018	$	4,927	$	5,989
Research and development expenses	$	108,987	$	96,436	$	100,531	$	102,724	$	118,463	$	106,686	$	99,048	$	110,369
Operating loss	$	(133,631)	$	(77,709)	$	(103,050)	$	(110,721)	$	(120,687)	$	(110,970)	$	(98,740)	$	(109,638)
Net loss	$	(138,651)	$	(80,000)	$	(108,586)	$	(117,203)	$	(119,632)	$	(110,286)	$	(98,585)	$	(112,164)
Net loss per share(1)
Basic	$	(0.78)	$	(0.45)	$	(0.61)	$	(0.65)	$	(0.69)	$	(0.63)	$	(0.56)	$	(0.64)
Diluted	$	(0.78)	$	(0.45)	$	(0.61)	$	(0.65)	$	(0.69)	$	(0.63)	$	(0.56)	$	(0.64)

_______________________________________________________________

(1)Quarterly income (loss) per share amounts may not total to the year-to-date income (loss) per share due to rounding.

Organization and Summary of Significant Accounting Policies (Detail) $ in Thousands, shares in Millions		12 Months Ended
	Apr. 13, 2020 USD ($)	Dec. 31, 2020 USD ($) reporting_unit shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 shares	Mar. 31, 2020 USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items]
Cash and investments in marketable securities		$ 1,198,558	$ 1,603,981
Net expense reimbursements from collaboration partner		38,700	24,000
Contract with customer, asset, reclassified to receivable		$ 200	12,800
Estimate for royalties resulting from net sales			$ 11,600
Number of reporting unit evaluated for goodwill \| reporting_unit		1
Purchase commitments related to contract manufacturing, clinical development and certain other items		$ 8,000
Weighted-average of potentially dilutive securities (stock options and RSUs) included in calculation of diluted securities under treasury stock method (in shares) \| shares				10.5
Accounts Receivable \| Customer Concentration Risk \| Partner One
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage revenue from customers			65.00%
Accounts Receivable \| Customer Concentration Risk \| Partner Two
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage revenue from customers			17.00%
Accounts Receivable \| Customer Concentration Risk \| Partner Three
Organization And Summary Of Significant Accounting Policies [Line Items]
Percentage revenue from customers			14.00%
NKTR - 181
Organization And Summary Of Significant Accounting Policies [Line Items]
Write off of prepayment					$ 19,700
Purchase commitments related to contract manufacturing, clinical development and certain other items					$ 25,500
7.75 Percent Senior Secured Notes Due October 2020 \| Senior Notes
Organization And Summary Of Significant Accounting Policies [Line Items]
Principal and interest repaid on senior notes	$ 254,800
Shares of Common Stock Underlying Outstanding Stock Options
Organization And Summary Of Significant Accounting Policies [Line Items]
Weighted average antidilutive securities excluded from computation of earnings per share \| shares				3.3
Stock Options and Restricted Stock Units
Organization And Summary Of Significant Accounting Policies [Line Items]
Weighted average antidilutive securities excluded from computation of earnings per share \| shares		17.4	17.9
Manufacturing equipment \| Minimum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives		3 years
Manufacturing equipment \| Maximum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives		10 years
Buildings
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives		20 years

Cash and Investments in Marketable Securities - Cash and Investments in Marketable Securities, Including Cash Equivalents (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	$ 198,955	$ 96,363
Short-term investments	862,941	1,228,499
Long-term investments	136,662	279,119
Total cash and investments in marketable securities	$ 1,198,558	$ 1,603,981

Cash and Investments in Marketable Securities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash and Investments in Marketable Securities [Line Items]
Sales of investments	$ 41,700,000	$ 0	$ 11,963,000
Accrued interest receivable	5,100,000	6,500,000
Level 1 to level 2 transfers	0	0
Level 2 to level 1 transfers	0	0
Gross unrealized gains		2,100,000
Gross unrealized losses		300,000
Letter of credit	$ 8,100,000	$ 6,800,000
Minimum
Cash and Investments in Marketable Securities [Line Items]
Long term investment maturity period	1 year	1 year
Maximum
Cash and Investments in Marketable Securities [Line Items]
Long term investment maturity period	2 years	2 years

Cash and Investments in Marketable Securities - Portfolio of Cash and Investments in Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross Unrealized Gains		$ 2,100
Gross Unrealized Losses		(300)
Cash	$ 6,285	5,829
Total cash and investments in marketable securities	1,198,558	1,603,981
Fair Value Hierarchy Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	1,002,443
Gross Unrealized Gains	1,081
Gross Unrealized Losses	(176)
Fair Value	1,003,348	1,507,655
Corporate Notes and Bonds \| Fair Value Hierarchy Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	686,543
Gross Unrealized Gains	1,035
Gross Unrealized Losses	(109)
Fair Value	687,469	1,132,182
Commercial Paper \| Fair Value Hierarchy Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	313,520
Gross Unrealized Gains	44
Gross Unrealized Losses	(67)
Fair Value	313,497	375,473
Obligations of U.S. government agencies \| Fair Value Hierarchy Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Amortized Cost	2,380
Gross Unrealized Gains	2
Gross Unrealized Losses	0
Fair Value	2,382	0
Money Market Funds \| Fair Value Hierarchy Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	179,302	83,546
Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	$ 9,623	$ 6,951

Inventory (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Raw materials	$ 2,422	$ 1,673
Work-in-process	10,703	8,267
Finished goods	2,167	2,725
Total inventory	$ 15,292	$ 12,665

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	$ 193,450	$ 188,322
Less: accumulated depreciation	(138,488)	(127,875)
Depreciable property, plant and equipment, net	54,962	60,447
Construction-in-progress	4,700	5,218
Property, plant and equipment, net	59,662	65,665
Building and leasehold improvements
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	92,977	93,097
Laboratory equipment
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	40,121	36,623
Computer equipment and software
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	28,684	26,910
Manufacturing equipment
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	21,796	22,030
Furniture, fixtures, and other
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	$ 9,872	$ 9,662

Property, Plant and Equipment - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Depreciation and amortization expenses	$ 12.5	$ 11.0	$ 8.8

Senior Secured Notes (Detail) - USD ($)			12 Months Ended
Senior Secured Notes (Detail) - USD ($)	Apr. 13, 2020	Oct. 05, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Secured Notes [Line Items]
Principal amount repaid			$ 250,000,000	$ 0	$ 0
Senior Notes \| 7.75% Senior Secured Notes Due October 2020
Secured Notes [Line Items]
Senior secured notes, principal amount		$ 250,000,000.0
Senior secured notes, interest rate		7.75%
Issuance costs		$ 8,900,000
Debt discount on transaction and facility fees		$ 8,700,000
Principal amount repaid	$ 250,000,000.0
Interest Receivable	$ 4,800,000

Leases - Additional Information (Detail) $ in Thousands	12 Months Ended
Leases - Additional Information (Detail) $ in Thousands	Dec. 31, 2020 USD ($) ft²	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Leases [Line Items]
Operating lease cost \| $	$ 18,985	$ 14,697	$ 7,972
Operating lease, payments \| $	$ 16,200	$ 8,400
Weighted average remaining lease term	9 years 1 month 6 days
Weighted average discount rate, percent	5.90%
Mission Bay Lease
Leases [Line Items]
Lease space (in sq ft) \| ft²	153,203
Third Street Lease
Leases [Line Items]
Lease space (in sq ft) \| ft²	135,936

Leases - Operating Lease Information (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) ft² term	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($)
Leases [Line Items]
Operating lease right-of-use assets recognized in exchange for lease liabilities	$ 2,133	$ 57,691	$ 0
Mission Bay Lease
Leases [Line Items]
Leased space delivered (in sq ft) \| ft²	4,940	13,907
Operating lease right-of-use assets recognized in exchange for lease liabilities	$ 2,133	$ 6,698
Number of consecutive terms to extend lease \| term	2
Lease extension term	5 years
Third Street Lease
Leases [Line Items]
Leased space delivered (in sq ft) \| ft²	0	67,105
Operating lease right-of-use assets recognized in exchange for lease liabilities	$ 0	$ 50,993
Number of consecutive terms to extend lease \| term	1
Lease extension term	5 years

Leases - Schedule of Lease Cost (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Operating lease cost	$ 18,985	$ 14,697	$ 7,972
Variable lease cost	8,179	6,408	4,497
Total lease costs	$ 27,164	$ 21,105	$ 12,469

Leases - Future Minimum Lease Payments for Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
2021	$ 17,938
2022	20,141
2023	20,780
2024	21,439
2025	22,117
2026 and thereafter	97,764
Total lease payments	200,179
Less: portion representing interest	(46,380)
Less: lease incentives	(3,511)
Operating lease liabilities	150,288
Less: current portion	(13,915)	$ (12,516)
Operating lease liabilities, less current portion	$ 136,373	$ 142,730

Liabilities Related to the Sales of Future Royalties - Additional Information (Detail) - USD ($) $ in Thousands					1 Months Ended		12 Months Ended			106 Months Ended
	Dec. 31, 2020	Dec. 30, 2020	Dec. 16, 2020	Feb. 24, 2012	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Liability Related to the Sale of Future Royalties [Line Items]
Royalty agreement contingent payment description							As a result of worldwide net sales of MIRCERA® for the 12 month periods ended December 31, 2013 and 2012 not reaching certain minimum thresholds.
Non-cash royalty revenue							$ 48,563	$ 36,303	$ 33,308	$ 255,705
Non-cash interest expense on liability related to sale of future royalties							30,267	$ 25,044	$ 21,196	196,960
Purchase and Sale Agreement 2012
Liability Related to the Sale of Future Royalties [Line Items]
Proceeds from sale of royalty rights				$ 124,000
Transaction costs related to sale of potential future royalties				$ 4,400
Non-cash royalty revenue							37,938			245,080
Non-cash interest expense on liability related to sale of future royalties							30,267			$ 196,960
Purchase and Sale Agreement 2020
Liability Related to the Sale of Future Royalties [Line Items]
Proceeds from sale of royalty rights		$ 150,000
Transaction costs related to sale of potential future royalties		$ 3,800
Non-cash royalty revenue	$ 10,625						10,625
Non-cash interest expense on liability related to sale of future royalties	$ 0						$ 0
Payment of transaction related to purchase and sale agreement			$ 210,000
Payment of transaction related to purchase and sale agreement if threshold is not achieved			240,000
Minimum transaction royalties payments needed to pay the difference between the 2025 threshold and 2020 transaction royalties			$ 208,000
Purchase and Sale Agreement with RPI
Liability Related to the Sale of Future Royalties [Line Items]
Payment made for milestone not achieved year two					$ 7,000
Payment made for milestone not achieved year one						$ 3,000

Liabilities Related to the Sales of Future Royalties - Summary of Liability Related to Potential Future Royalties (Detail) - USD ($) $ in Thousands		12 Months Ended			106 Months Ended
	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2020
Liability Related to the Sale of Future Royalties [Line Items]
Liability related to the sale of future royalties—beginning balance		$ 73,551			$ 0
Royalty monetization proceeds		150,000			274,000
Non-cash royalty revenue		48,563	$ 36,303	$ 33,308	255,705
Non-cash interest expense		30,267	25,044	$ 21,196	196,960
Payments to RPI		0			(10,000)
Liability related to the sale of future royalties – ending balance	$ 205,255	205,255	73,551		205,255
Less: unamortized transaction costs	(4,915)	(4,915)			(4,915)
Liability related to the sale of future royalties, net	200,340	200,340	72,020		200,340
Purchase and Sale Agreement 2012
Liability Related to the Sale of Future Royalties [Line Items]
Liability related to the sale of future royalties—beginning balance		73,551			0
Royalty monetization proceeds		0			124,000
Non-cash royalty revenue		37,938			245,080
Non-cash interest expense		30,267			196,960
Payments to RPI		0			(10,000)
Liability related to the sale of future royalties – ending balance	65,880	65,880	$ 73,551		65,880
Less: unamortized transaction costs	(1,165)	(1,165)			(1,165)
Liability related to the sale of future royalties, net	64,715	$ 64,715			64,715
Implicit interest rate over the life of the agreement		20.20%	19.50%	18.70%
Prospective effective interest rate		48.00%	38.00%	29.00%
Purchase and Sale Agreement 2020
Liability Related to the Sale of Future Royalties [Line Items]
Liability related to the sale of future royalties—beginning balance	0	$ 0
Royalty monetization proceeds	150,000	150,000
Non-cash royalty revenue	10,625	10,625
Non-cash interest expense	0	0
Payments to RPI	0	0
Liability related to the sale of future royalties – ending balance	139,375	139,375	$ 0		139,375
Less: unamortized transaction costs	(3,750)	(3,750)			(3,750)
Liability related to the sale of future royalties, net	$ 135,625	$ 135,625			$ 135,625
Implicit interest rate over the life of the agreement				16.00%
Prospective effective interest rate				16.00%

Commitments and Contingencies (Detail) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Loss Contingencies [Line Items]
Purchase commitments related to contract manufacturing, clinical development and certain other items	$ 8,000,000.0
Legal Matters
Loss Contingencies [Line Items]
Litigation matters, liabilities	0	$ 0
Indemnification Obligation
Loss Contingencies [Line Items]
Litigation matters, liabilities	0	0
Commercial Agreements
Loss Contingencies [Line Items]
Litigation matters, liabilities	0	$ 0
Merger and Acquisition Related Claims \| Maximum
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	10,000,000.0
Securities Related Claims
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	10,000,000.0
Non-Securities Related Claims
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	$ 10,000,000.0

Stockholders' Equity (Detail)				12 Months Ended
Stockholders' Equity (Detail)	Jun. 17, 2020 shares	Jun. 26, 2018 shares	Apr. 03, 2018 shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Dec. 31, 2018 USD ($) shares
Class of Stock [Line Items]
Stock issued during period subject to lock-up and stand-still provisions period			5 years
Number of shares to be issued upon exercise of outstanding options or vesting of RSUs				20,894,000
Common stock, shares authorized (in shares)				300,000,000	300,000,000
Maximum 401(k) per employee, percentage of annual salary				60.00%
Matching 401(k) employer contribution, maximum amount \| $				$ 6,000
Compensation expense in connection with 401(k) retirement plan \| $				$ 3,500,000	$ 3,500,000	$ 2,800,000
Change in control severance payment period for executives				12 months
Change in control severance payment period for Chief Executive Officer				24 months
Change in control severance payment period for senior vice presidents and vice presidents				12 months
Change in control severance payment period for employees				6 months
Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock, shares authorized (in shares)				2,500,000
Percentage of purchase price of stock				85.00%
Employee Stock Purchase Plan
Class of Stock [Line Items]
Increase in aggregate number of shares authorized (in shares)	1,000,000
2017 Performance Incentive Plan
Class of Stock [Line Items]
Number of shares available for issuance under equity compensation plans				7,569,000
Number of common stock shares available for stock options grants				8,300,000
Number of additional shares available for award grants		10,900,000
Share-based compensation plan's share limit reduction for every one restricted stock unit granted (in shares)				1.5
Stock options term under equity incentive plans				8 years
Employee Stock Purchase Plan
Class of Stock [Line Items]
Number of shares available for issuance under equity compensation plans				1,321,000
Amended and Restated 2017 Plan
Class of Stock [Line Items]
Increase in aggregate number of shares authorized (in shares)	10,000,000
Common Stock
Class of Stock [Line Items]
Sale of common stock (in shares)			8,284,600			8,285,000
Common stock, shares reserved for issuance in equity compensation plans				29,784,000
Employee \| 2017 Performance Incentive Plan \| Shares of Common Stock Underlying Outstanding Stock Options
Class of Stock [Line Items]
Service period for stock-based compensation award granted				4 years
Employee \| 2017 Performance Incentive Plan \| RSUs and PSUs
Class of Stock [Line Items]
Service period for stock-based compensation award granted				3 years
Director \| 2017 Performance Incentive Plan \| Shares of Common Stock Underlying Outstanding Stock Options
Class of Stock [Line Items]
Service period for stock-based compensation award granted				1 year
Director \| 2017 Performance Incentive Plan \| RSUs and PSUs
Class of Stock [Line Items]
Service period for stock-based compensation award granted				1 year

License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 55,849	$ 16,975	$ 1,097,265
Bristol-Myers Squibb \| Bempegaldesleukin
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	50,000	0	1,059,768
Eli Lilly and Company \| NKTR-358
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,259	7,019	11,634
Amgen, Inc. \| Neulasta
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	4,167	5,000	5,000
Baxalta Incorporated / Takeda \| Hemophilia, Including ADYNOVATE and ADYNOVITM
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	346	378	20,328
Other
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 77	$ 4,578	$ 535

License and Collaboration Agreements - Additional Information (Detail)			1 Months Ended								3 Months Ended								12 Months Ended
	Feb. 13, 2018	Aug. 23, 2017 USD ($)	Apr. 30, 2018 USD ($) shares	Jan. 31, 2018 USD ($)	Nov. 30, 2017 USD ($)	Sep. 30, 2017 USD ($)	Aug. 31, 2017 USD ($)	Sep. 30, 2016	Mar. 31, 2016	Oct. 31, 2010 USD ($)	Dec. 31, 2020 USD ($)	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Jan. 09, 2020 USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Performance obligation recognized																			$ 129,600,000	$ 77,500,000	$ 95,300,000
Potential future additional payments for development milestones											$ 1,700,000,000								1,700,000,000
Accounts receivable											38,889,000				$ 36,802,000				38,889,000	36,802,000
Other long-term liabilities											6,516,000				768,000				6,516,000	768,000
Development milestones received																			5,516,000
Deferred revenue											2,555,000				8,071,000				2,555,000	8,071,000
Revenue recognized from contracts with customers											23,462,000	$ 30,033,000	$ 48,847,000	$ 50,573,000	33,862,000	$ 29,218,000	$ 23,315,000	$ 28,222,000	$ 152,915,000	114,617,000	1,193,323,000
Percentage of net sales to fund external costs incurred, due to reduction of 2 percentage points																			0.02
BMS Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Sales milestone revenue																			$ 50,000,000.0
NKTR-358 \| Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue											0								$ 0
Regulatory milestones payment, description																			A portion of the development milestones may be reduced by 50% under certain conditions, related to the final formulation of the approved product and the timing of prior approval (if any) of competitive products with a similar mechanism of action, which could reduce these milestone payments by 75% if both conditions occur.
Bristol Myers Squibb Collaboration Agreement \| Nektar 214 \| Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Global commercialization profits and losses sharing percentage	65.00%
Percentage of sharing production costs	65.00%
Upfront and milestone payments received from license agreements			$ 1,000,000,000.0
Maximum total additional cash payments receivable upon achievement of certain development and regulatory milestones																			$ 1,455,000,000
Bristol Myers Squibb Collaboration Agreement \| Nektar 214 \| Nektar's \| Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Eligible additional cash payments receivable upon achievement of certain sales milestones			$ 350,000,000.0
Bristol Myers Squibb Collaboration Agreement \| Nektar 214 \| Nektar's \| Opdivo
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	32.50%
Nektar-358 \| Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment						$ 150,000,000.0
Percentage of sharing in Phase 2 development costs		25.00%
Nektar
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of upfront payment, market access milestones, royalties and sales milestones									40.00%
Eli Lilly \| Nektar-358
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing in Phase 2 development costs		75.00%
Bristol-Myers Squibb \| Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Shares issued (in shares) \| shares			8,284,600
Sale of stock consideration received			$ 850,000,000.0
Bristol-Myers Squibb \| Nektar 214 \| Research and development
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement of expenses																			128,200,000	105,400,000	62,500,000
Bristol-Myers Squibb \| BMS Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Accounts receivable											38,700,000				$ 24,000,000.0				38,700,000	$ 24,000,000.0
Company share of development costs, annual cap																			125,000,000.0
Company share of development costs																			129,000,000.0
Development costs exceeded																			4,000,000.0
Reimbursement recognized																			4,000,000.0
Other long-term liabilities											$ 4,000,000.0								4,000,000.0
Bristol-Myers Squibb \| Clinical Trial Agreement \| Nektar 214
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of out-of-pocket costs to be reimbursed by partner								50.00%
Bristol-Myers Squibb \| Bristol Myers Squibb Collaboration Agreement \| Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total consideration received under agreements																					1,850,000,000
Estimated fair value of shares																					790,200,000
Remaining amount allocated to transaction price																			$ 25,000,000.0		1,059,800,000
Potential future development, regulatory and sales milestones																					$ 1,800,000,000
Bristol-Myers Squibb \| Bristol Myers Squibb Collaboration Agreement \| Nektar 214
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Global commercialization profits and losses sharing percentage	35.00%
Percentage of sharing production costs	35.00%
Bristol-Myers Squibb \| Bristol Myers Squibb Collaboration Agreement \| Nektar 214 \| Opdivo
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	67.50%
Baxalta Incorporated / Takeda \| Hemophilia
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Received under right to sublicense agreement					$ 12,000,000.0
Baxalta Incorporated / Takeda \| Hemophilia \| Annual Sales Level Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized from contracts with customers																		$ 10,000,000.0
Baxalta Incorporated / Takeda \| Hemophilia \| European Union
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized from contracts with customers				$ 10,000,000.0
Eli Lilly and Company \| Nektar-358
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount of transaction price allocated to performance obligation						125,900,000
Revenue recognized from contracts with customers							$ 125,900,000
Eli Lilly and Company \| Nektar-358 \| Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future additional development and regulatory milestones		$ 250,000,000.0
Eli Lilly and Company \| Nektar-358 \| Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of regulatory milestones payments will be reduced under certain conditions		50.00%
Percentage of regulatory milestones payments will be reduced if conditions occur		75.00%
Eli Lilly and Company \| Nektar-358 \| Nektar's \| Maximum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of funding phase 3 development costs on an indication by indication basis borne		25.00%
Eli Lilly and Company \| Nektar-358 \| Nektar's \| Minimum
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of funding phase 3 development costs on an indication by indication basis borne		0.00%
Eli Lilly and Company \| Phase 1 Clinical Development \| Nektar-358
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount of transaction price allocated to performance obligation						17,600,000
Eli Lilly and Company \| Drug Product Development \| Nektar-358
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount of transaction price allocated to performance obligation						$ 6,500,000
Amgen, Inc.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment										$ 50,000,000.0
Astra Zeneca Ab \| MOVANTIK and MOVENTIG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of net sales to fund external costs incurred											0.33								0.33
Amount of net sales to fund external costs incurred cap																			$ 35,000,000.0
Astra Zeneca Ab \| MOVANTIK and MOVENTIG \| Upfront Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment																						$ 37,600,000	$ 385,000,000.0
Astra Zeneca Ab \| AstraZeneca-Kirin
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue											$ 0								0
Percentage of upfront payment, market access milestone payments, royalties and sales milestone payments from sublicense agreement retained by our collaboration partner									60.00%
Other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future additional payments for development milestones											40,000,000.0								40,000,000.0
Terminated Partnership
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue											$ 2,000,000.0								$ 2,000,000.0
Milestone One \| Bristol Myers Squibb Collaboration Agreement \| Nektar 214 \| Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential future additional payments for development milestones																								$ 25,000,000.0

License and Collaboration Agreements - Changes in Deferred Revenue Balance from Collaboration Agreements (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred revenue, Beginning balance	$ 8,071
Recognition of previously unearned revenue	(5,516)
Deferred revenue, Ending balance	$ 2,555

Stock-Based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 94,261	$ 99,795	$ 88,101
Cost of goods sold
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	2,825	4,294	4,629
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	57,116	63,224	56,193
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	33,295	32,277	27,279
Impairment of assets and other costs for terminated program
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 1,025	$ 0	$ 0

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation costs	$ 193.7
Recognized over a weighted-average period	1 year 9 months 14 days
Dividend yield	0.00%	0.00%	0.00%
Total intrinsic value of options exercised	$ 15.9	$ 30.6	$ 303.4
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%
Restricted Stock Units (RSU)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock vested	$ 33.3	$ 32.4	$ 80.4

Stock-Based Compensation - Black-Scholes Option-Pricing Model Assumptions Used to Calculate Fair Value of Employee Stock Options (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement [Abstract]
Average risk-free interest rate	0.40%	1.80%	2.80%
Dividend yield	0.00%	0.00%	0.00%
Average volatility factor	64.10%	62.20%	61.00%
Average weighted average expected life	5 years 7 months 6 days	5 years 7 months 6 days	5 years 1 month 6 days
Weighted-average grant-date fair value (in dollars per share)	$ 10.70	$ 12.25	$ 29.86

Stock-Based Compensation - Stock Option Activity Under Equity Incentive Plans (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares
Share-based Payment Arrangement [Abstract]
Number of shares, outstanding, beginning balance (in shares) \| shares	14,885
Number of shares, options granted (in shares) \| shares	1,654
Number of shares, options exercised (in shares) \| shares	(1,669)
Number of shares, options forfeited and canceled (in shares) \| shares	(1,233)
Number of shares, outstanding, ending balance (in shares) \| shares	13,637
Number of shares, exercisable (in shares) \| shares	9,523
Weighted-Average Exercise Price per Share, outstanding, beginning balance (in dollars per share) \| $ / shares	$ 25.23
Weighted-Average Exercise Price per Share, options granted (in dollars per share) \| $ / shares	19.15
Weighted-Average Exercise Price per Share, options exercised (in dollars per share) \| $ / shares	11.69
Weighted-Average Exercise Price per Share, options forfeited and canceled (in dollars per share) \| $ / shares	45.70
Weighted-Average Exercise Price per Share, outstanding, ending balance (in dollars per share) \| $ / shares	24.30
Weighted-Average Exercise Price per Share, exercisable (in dollars per share) \| $ / shares	$ 22.99
Weighted-Average Remaining Contractual Life, outstanding	3 years 11 months 15 days
Weighted-Average Remaining Contractual Life, exercisable	2 years 8 months 15 days
Aggregate Intrinsic Value, outstanding \| $	$ 23,478
Aggregate Intrinsic Value, exercisable \| $	$ 23,468

Stock-Based Compensation - Restricted Stock Unit Award Activity (Detail) - Restricted Stock Units (RSU) shares in Thousands	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units Issued, Beginning balance (in shares) \| shares	4,935
Granted (in shares) \| shares	4,686
Vested and released (in shares) \| shares	(1,661)
Forfeited and canceled (in shares) \| shares	(866)
Units Issued, Ending balance (in shares) \| shares	7,094
Weighted Average Grant Date Fair Value, Beginning balance (in dollars per share) \| $ / shares	$ 30.85
Weighted Average Grant Date Fair Value, Granted (in dollars per share) \| $ / shares	19.24
Weighted Average Grant Date Fair Value, Vested and released (in dollars per share) \| $ / shares	34.83
Weighted Average Grant Date Fair Value, Forfeited and canceled (in dollars per share) \| $ / shares	29.66
Weighted Average Grant Date Fair Value, Ending balance (in dollars per share) \| $ / shares	$ 22.46

Income Taxes - Income (Loss) Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Domestic	$ (445,370)	$ (441,494)	$ 680,423
Foreign	1,423	1,440	2,302
Income (loss) before provision for income taxes	$ (443,947)	$ (440,054)	$ 682,725

- Definition

Amount of income (loss) from continuing operations, including income (loss) from equity method investments, before deduction of income tax expense (benefit), and income (loss) attributable to noncontrolling interest.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 940
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68072869&loc=d3e41242-110953

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(10))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(8))
-URI http://asc.fasb.org/extlink&oid=120400993&loc=SL114874131-224263

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 235
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-05(b)(2))
-URI http://asc.fasb.org/extlink&oid=120399901&loc=d3e537907-122884

Reference 9: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 31
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8924-108599

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(15))
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

+ Details

Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Federal	$ 0	$ 0	$ 0
State	165	139	699
Foreign	364	495	620
Total Current	529	634	1,319
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	(36)	(21)	93
Total Deferred	(36)	(21)	93
Provision for income taxes	$ 493	$ 613	$ 1,412

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes Disclosure [Line Items]
Statutory income tax rate			21.00%
Valuation allowance, increase (decrease) amount	$ (95,000,000.0)	$ (114,600,000)
Income tax research credits	$ 3,081,000	10,511,000	$ 17,295,000
Unrecognized tax benefits, period may increase or decrease due to tax examination	12 months
Unrecognized tax benefits, interest recognized	$ 0	0	0
Unrecognized tax benefits, penalties recognized	0	$ 0	$ 0
Federal
Income Taxes Disclosure [Line Items]
Net operating loss carryforward for income tax	2,000,000,000.0
Income tax research credits	98,900,000
Federal orphan drug credits	17,700,000
State
Income Taxes Disclosure [Line Items]
Net operating loss carryforward for income tax	1,300,000,000
Income tax research credits	$ 44,000,000.0

Income Taxes - Income Tax Provision Related to Continuing Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income tax expense (benefit) at federal statutory rate	$ (93,229)	$ (92,411)	$ 143,372
Research credits	(3,081)	(10,511)	(17,295)
Premium on equity issuance	0	0	(12,551)
Change in valuation allowance	87,060	104,440	(46,885)
Stock-based compensation	7,929	(672)	(66,716)
Non-cash royalty revenue related to sale of future royalties	(7,967)	(7,624)	(6,995)
Non-cash interest expense on liability related to sale of future royalties	6,356	5,259	4,451
Other	3,425	2,132	4,031
Provision for income taxes	$ 493	$ 613	$ 1,412

Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 456,284	$ 399,361
Research and other credits	132,994	128,015
Operating lease liabilities	35,672	36,907
Liability related to the sale of future royalties	32,737	0
Stock-based compensation	32,517	30,875
Other	11,688	13,568
Deferred tax assets before valuation allowance	701,892	608,726
Valuation allowance for deferred tax assets	(670,103)	(575,087)
Total deferred tax assets	31,789	33,639
Deferred tax liabilities:
Operating lease right-of-use assets	(29,707)	(31,718)
Other	(1,856)	(1,725)
Total deferred tax liabilities	(31,563)	(33,443)
Net deferred tax assets	$ 226	$ 196

Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 77,410	$ 27,419	$ 20,483
Tax positions related to current year, Additions	2,512	49,858	5,664
Reductions	0	0	0
Tax positions related to prior year, Additions	193	277	1,272
Reductions	(1,450)	(144)	0
Settlements	0	0	0
Lapses in statute of limitations	0	0	0
Ending balance	$ 78,665	$ 77,410	$ 27,419

Segment Reporting - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)	Dec. 31, 2018
Segment Reporting Information [Line Items]
Number of operating business segment \| segment	1
Property, plant and equipment, net	$ 59,662	$ 65,665
United States
Segment Reporting Information [Line Items]
Property, plant and equipment, net	54,500	59,700
India
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 5,100	$ 5,300
Revenue \| BMS \| Customer Concentration Risk
Segment Reporting Information [Line Items]
Percentage revenue from customers	33.00%		89.00%
Revenue \| UCB \| Customer Concentration Risk
Segment Reporting Information [Line Items]
Percentage revenue from customers	23.00%	28.00%
Revenue \| Baxalta Incorporated / Takeda \| Customer Concentration Risk
Segment Reporting Information [Line Items]
Percentage revenue from customers	14.00%	19.00%
Revenue \| Astra Zeneca Ab \| Customer Concentration Risk
Segment Reporting Information [Line Items]
Percentage revenue from customers	13.00%	17.00%
Property, Plant and Equipment \| Geographic Concentration Risk \| United States
Segment Reporting Information [Line Items]
Percentage revenue from customers	91.00%	92.00%
Property, Plant and Equipment \| Geographic Concentration Risk \| India
Segment Reporting Information [Line Items]
Percentage revenue from customers	9.00%	8.00%

Segment Reporting - Revenue by Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenue by geographic area
Total revenue	$ 23,462	$ 30,033	$ 48,847	$ 50,573	$ 33,862	$ 29,218	$ 23,315	$ 28,222	$ 152,915	$ 114,617	$ 1,193,323
United States \| Reportable Geographical Components
Revenue by geographic area
Total revenue									64,966	27,093	1,090,794
Non-US \| Reportable Geographical Components
Revenue by geographic area
Total revenue									$ 87,949	$ 87,524	$ 102,529

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 40
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9031-108599

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9038-108599

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8933-108599

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130543-203045

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8736-108599

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 42
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130545-203045

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

+ Details

Subsequent Event (Details) - Subsequent Event - SFJ Pharmaceuticals $ in Millions	Feb. 12, 2021 USD ($)
Subsequent Event [Line Items]
Committed funding	$ 150.0
Success-based payments, first indication	$ 450.0
Success-based payments, first indication, period to be paid	5 years
Success-based payments, second indication	$ 150.0
Success-based payments, second indication, period to be paid	7 years
Additional indication payment	$ 37.5

Selected Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Selected Quarterly Financial Data [Line Items]
Total revenue	$ 23,462	$ 30,033	$ 48,847	$ 50,573	$ 33,862	$ 29,218	$ 23,315	$ 28,222	$ 152,915	$ 114,617	$ 1,193,323
Cost of goods sold	4,323	5,570	5,773	3,811	5,989	4,927	5,018	5,440	19,477	21,374	24,412
Research and development expenses	102,724	100,531	96,436	108,987	110,369	99,048	106,686	118,463	408,678	434,566	399,536
Operating loss	(110,721)	(103,050)	(77,709)	(133,631)	(109,638)	(98,740)	(110,970)	(120,687)	(425,111)	(440,035)	687,932
Net income (loss)	$ (117,203)	$ (108,586)	$ (80,000)	$ (138,651)	$ (112,164)	$ (98,585)	$ (110,286)	$ (119,632)	$ (444,440)	$ (440,667)	$ 681,313
Net income (loss) per share
Basic ( in dollars per share)	$ (0.65)	$ (0.61)	$ (0.45)	$ (0.78)	$ (0.64)	$ (0.56)	$ (0.63)	$ (0.69)	$ (2.49)	$ (2.52)	$ 4.02
Diluted (in dollars per share)	$ (0.65)	$ (0.61)	$ (0.45)	$ (0.78)	$ (0.64)	$ (0.56)	$ (0.63)	$ (0.69)	$ (2.49)	$ (2.52)	$ 3.78
Product Sales
Selected Quarterly Financial Data [Line Items]
Total revenue	$ 2,884	$ 5,691	$ 5,485	$ 3,444	$ 5,815	$ 5,558	$ 4,346	$ 4,398	$ 17,504	$ 20,117	$ 20,774