Cover Page - shares	9 Months Ended
Cover Page - shares	Sep. 30, 2019	Nov. 01, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		175,922,206
Amendment Flag	false
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Central Index Key	0000906709
Current Fiscal Year End Date	--12-31

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 81,224	$ 194,905
Short-term investments	1,414,448	1,140,445
Accounts receivable	41,205	43,213
Inventory	13,720	11,381
Advance payments to contract manufacturers	13,015	26,450
Other current assets	15,212	21,293
Total current assets	1,578,824	1,437,687
Long-term investments	231,082	582,889
Property, plant and equipment, net	64,614	48,851
Operating lease right-of-use assets	134,888	0
Goodwill	76,501	76,501
Other assets	2,385	4,244
Total assets	2,088,294	2,150,172
Current liabilities:
Accounts payable	21,963	5,854
Accrued compensation	23,101	9,937
Accrued clinical trial expenses	38,338	14,700
Accrued contract manufacturing expenses	8,646	23,841
Other accrued expenses	11,394	9,580
Interest payable	4,198	4,198
Operating lease liabilities, current portion	9,318	0
Deferred revenue, current portion	8,392	13,892
Total current liabilities	125,350	82,002
Senior secured notes, net	248,257	246,950
Operating lease liabilities, less current portion	145,099	0
Liability related to the sale of future royalties, net	73,455	82,911
Deferred revenue, less current portion	6,779	10,744
Other long-term liabilities	643	9,990
Total liabilities	599,583	432,597
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares designated or outstanding at September 30, 2019 or December 31, 2018	0	0
Common stock, $0.0001 par value; 300,000 shares authorized; 175,786 shares and 173,530 shares outstanding at September 30, 2019 and December 31, 2018, respectively	17	17
Capital in excess of par value	3,241,160	3,147,925
Accumulated other comprehensive loss	(1,186)	(6,316)
Accumulated deficit	(1,751,280)	(1,424,051)
Total stockholders’ equity	1,488,711	1,717,575
Total liabilities and stockholders’ equity	$ 2,088,294	$ 2,150,172

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars 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 outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares outstanding (in shares)	175,786,000	173,530,000

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue:
Total revenue	$ 29,218	$ 27,762	$ 80,755	$ 1,153,497
Operating costs and expenses:
Cost of goods sold	4,927	4,783	15,385	16,951
Research and development	99,048	102,895	324,197	290,653
General and administrative	23,983	18,718	71,570	57,666
Total operating costs and expenses	127,958	126,396	411,152	365,270
Income (loss) from operations	(98,740)	(98,634)	(330,397)	788,227
Non-operating income (expense):
Interest expense	(5,425)	(5,442)	(15,882)	(16,167)
Non-cash interest expense on liability related to sale of future royalties	(5,813)	(4,814)	(17,853)	(14,808)
Interest income and other income (expense), net	11,492	11,847	35,964	25,523
Total non-operating income (expense), net	254	1,591	2,229	(5,452)
Income (loss) before provision for income taxes	(98,486)	(97,043)	(328,168)	782,775
Provision (benefit) for income taxes	322	(900)	(939)	3,250
Net income (loss)	$ (98,808)	$ (96,143)	$ (327,229)	$ 779,525
Net income (loss) per share
Basic (in dollars per share)	$ (0.56)	$ (0.56)	$ (1.87)	$ 4.63
Diluted (in dollars per share)	$ (0.56)	$ (0.56)	$ (1.87)	$ 4.34
Weighted average shares outstanding used in computing net income (loss) per share
Basic (in shares)	175,402	172,698	174,609	168,363
Diluted (in shares)	175,402	172,698	174,609	179,619
Product sales
Revenue:
Total revenue	$ 5,558	$ 4,256	$ 14,302	$ 16,414
Royalty revenue
Revenue:
Total revenue	10,275	10,259	29,008	29,898
Non-cash royalty revenue related to sale of future royalties
Revenue:
Total revenue	10,264	8,372	27,585	24,337
License, collaboration and other revenue
Revenue:
Total revenue	$ 3,121	$ 4,875	$ 9,860	$ 1,082,848

Condensed Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Shares	Capital in Excess of Par Value	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2017		159,524,000
Beginning balance at Dec. 31, 2017	$ 87,828	$ 15	$ 2,207,865	$ (2,111)	$ (2,117,941)
Adoption of new accounting standards	12,577				12,577
Shares issued under equity compensation plans (in shares)		2,855,000
Shares issued under equity compensation plans	34,406	$ 1	34,405
Stock-based compensation	19,949		19,949
Other comprehensive loss	(685)			(685)
Net loss	(95,792)				(95,792)
Ending balance (in shares) at Mar. 31, 2018		162,379,000
Ending balance at Mar. 31, 2018	58,283	$ 16	2,262,219	(2,796)	(2,201,156)
Beginning balance (in shares) at Dec. 31, 2017		159,524,000
Beginning balance at Dec. 31, 2017	$ 87,828	$ 15	2,207,865	(2,111)	(2,117,941)
Shares issued under equity compensation plans (in shares)	5,248,000
Net loss	$ 779,525
Ending balance (in shares) at Sep. 30, 2018		173,057,000
Ending balance at Sep. 30, 2018	1,790,122	$ 17	3,121,322	(5,378)	(1,325,839)
Beginning balance (in shares) at Mar. 31, 2018		162,379,000
Beginning balance at Mar. 31, 2018	58,283	$ 16	2,262,219	(2,796)	(2,201,156)
Sale of stock to Bristol-Myers Squibb (in shares)		8,285,000
Sale of stock to Bristol-Myers Squibb	790,231	$ 1	790,230	0	0
Shares issued under equity compensation plans (in shares)		1,751,000
Shares issued under equity compensation plans	20,987		20,987
Stock-based compensation	20,659		20,659
Other comprehensive loss	(1,206)			(1,206)
Net loss	971,460				971,460
Ending balance (in shares) at Jun. 30, 2018		172,415,000
Ending balance at Jun. 30, 2018	$ 1,860,414	$ 17	3,094,095	(4,002)	(1,229,696)
Shares issued under equity compensation plans (in shares)	642,000	642,000
Shares issued under equity compensation plans	$ 3,940		3,940
Stock-based compensation	23,287		23,287
Other comprehensive loss	(1,376)			(1,376)
Net loss	(96,143)				(96,143)
Ending balance (in shares) at Sep. 30, 2018		173,057,000
Ending balance at Sep. 30, 2018	1,790,122	$ 17	3,121,322	(5,378)	(1,325,839)
Beginning balance (in shares) at Dec. 31, 2018		173,530,000
Beginning balance at Dec. 31, 2018	1,717,575	$ 17	3,147,925	(6,316)	(1,424,051)
Shares issued under equity compensation plans (in shares)		698,000
Shares issued under equity compensation plans	5,463		5,463
Stock-based compensation	25,385		25,385
Other comprehensive loss	3,600			3,600
Net loss	(118,512)				(118,512)
Ending balance (in shares) at Mar. 31, 2019		174,228,000
Ending balance at Mar. 31, 2019	1,633,511	$ 17	3,178,773	(2,716)	(1,542,563)
Beginning balance (in shares) at Dec. 31, 2018		173,530,000
Beginning balance at Dec. 31, 2018	$ 1,717,575	$ 17	3,147,925	(6,316)	(1,424,051)
Shares issued under equity compensation plans (in shares)	2,256,000
Net loss	$ (327,229)
Ending balance (in shares) at Sep. 30, 2019		175,786,000
Ending balance at Sep. 30, 2019	1,488,711	$ 17	3,241,160	(1,186)	(1,751,280)
Beginning balance (in shares) at Mar. 31, 2019		174,228,000
Beginning balance at Mar. 31, 2019	1,633,511	$ 17	3,178,773	(2,716)	(1,542,563)
Shares issued under equity compensation plans (in shares)		738,000
Shares issued under equity compensation plans	7,103		7,103
Stock-based compensation	24,522		24,522
Other comprehensive loss	1,928			1,928
Net loss	(109,909)				(109,909)
Ending balance (in shares) at Jun. 30, 2019		174,966,000
Ending balance at Jun. 30, 2019	$ 1,557,155	$ 17	3,210,398	(788)	(1,652,472)
Shares issued under equity compensation plans (in shares)	820,000	820,000
Shares issued under equity compensation plans	$ 5,882		5,882
Stock-based compensation	24,880		24,880
Other comprehensive loss	(398)			(398)
Net loss	(98,808)				(98,808)
Ending balance (in shares) at Sep. 30, 2019		175,786,000
Ending balance at Sep. 30, 2019	$ 1,488,711	$ 17	$ 3,241,160	$ (1,186)	$ (1,751,280)

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net income (loss)	$ (327,229)	$ 779,525
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	(27,585)	(24,337)
Non-cash interest expense on liability related to sale of future royalties	17,853	14,808
Stock-based compensation	74,787	63,895
Depreciation and amortization	9,582	7,799
Accretion of discounts, net and other non-cash transactions	(10,421)	(8,136)
Changes in operating assets and liabilities:
Accounts receivable	2,008	(16,179)
Inventory	(2,339)	(2,570)
Other assets	18,127	(22,087)
Accounts payable	16,109	2,611
Accrued compensation	13,164	19,659
Other accrued expenses	10,019	26,603
Deferred revenue	(9,465)	(10,931)
Other liabilities	11,932	5,104
Net cash provided by (used in) operating activities	(203,458)	835,764
Cash flows from investing activities:
Purchases of investments	(1,028,883)	(1,944,178)
Maturities of investments	1,122,902	467,658
Sales of investments	0	11,963
Purchases of property, plant and equipment	(22,614)	(5,552)
Sales of property, plant and equipment	0	2,633
Net cash provided by (used in) investing activities	71,405	(1,467,476)
Cash flows from financing activities:
Issuance of common stock	0	790,231
Proceeds from shares issued under equity compensation plans	18,449	59,067
Net cash provided by financing activities	18,449	849,298
Effect of exchange rates on cash and cash equivalents	(77)	(87)
Net increase (decrease) in cash and cash equivalents	(113,681)	217,499
Cash and cash equivalents at beginning of period	194,905	4,762
Cash and cash equivalents at end of period	81,224	222,261
Supplemental disclosures of cash flow information:
Cash paid for interest	14,229	14,701
Operating lease right-of-use assets recognized in exchange for lease liabilities	$ 56,025	$ 0

Organization and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
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 treatments for cancer, autoimmune disease and chronic pain. 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 September 30, 2019, we had approximately $1.7 billion in cash and investments in marketable securities and debt of $250.0 million in principal of senior secured notes due in October 2020. Basis of Presentation and Principles of Consolidation Our consolidated financial statements include the financial position, results of operations and cash flows of our wholly-owned subsidiaries: Inheris Biopharma, Inc., Nektar Therapeutics (India) Private Limited (Nektar India) and Nektar Therapeutics UK Limited. We have eliminated all intercompany accounts and transactions in consolidation. We prepared our Condensed Consolidated Financial Statements following the requirements of the Securities and Exchange Commission (SEC) for interim reporting. As permitted under those rules, we may condense or omit certain footnotes or other financial information that are normally required by U.S. generally accepted accounting principles (GAAP) for annual periods. In the opinion of management, these financial statements include all normal and recurring adjustments that we consider necessary for the fair presentation of our financial position and operating results. Our Condensed 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 Condensed 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, neither of which were significant during the three and nine months ended September 30, 2019 and 2018. In addition, there were no significant reclassifications out of accumulated other comprehensive loss to the statements of operations during the three and nine months ended September 30, 2019 and 2018. The accompanying Condensed Consolidated Financial Statements are unaudited. The Condensed Consolidated Balance Sheet data as of December 31, 2018 was derived from the audited consolidated financial statements which are included in our Annual Report on Form 10-K for the year ended December 31, 2018 filed with the SEC on March 1, 2019. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the consolidated financial statements and the accompanying notes to those financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2018. Revenue, expenses, assets, and liabilities can vary during each quarter of the year. The results and trends in these interim Condensed Consolidated Financial Statements are not necessarily indicative of the results to be expected for the full year or any other period. Use of Estimates The preparation of consolidated financial statements in conformity with 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. As appropriate, we assess our estimates each period, update them to reflect current information and generally recognize any changes in such estimates in the period first identified. Segment Information We operate in one business segment which focuses on applying our technology platform 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. Significant Concentrations Our customers are primarily pharmaceutical and biotechnology companies that are 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, other contingent payments and royalties, as well as reimbursable costs from collaborative research and development agreements. As of September 30, 2019 and December 31, 2018, our accounts receivable includes $27.7 million and $24.2 million, respectively, for net expense reimbursements from our collaboration partner Bristol-Myers Squibb Company (BMS). 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, our ability to develop and produce our drug candidates 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 three and nine months ended September 30, 2019 under ASC 842. We have not restated the results for the three and nine months ended September 30, 2018 and our financial position as of December 31, 2018, and 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 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 real estate 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. As a result of our adoption of ASC 842, we recorded right-of-use assets of $83.5 million and lease liabilities of $96.2 million for our facilities operating leases, with no effect on our opening balance of accumulated deficit. Please see Note 4 for additional information regarding our leases. 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. 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, we are entitled to royalties from our collaboration partners based on the net sales of their approved drugs that are marketed and sold in one or more countries where we hold royalty rights. For arrangements that include sales-based royalties, including commercial milestone payments based on the level of sales, we have concluded that the license is the predominant item to which the royalties relate. 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 or filing for or receipt of regulatory approval, 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. 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. 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 clinical 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 our 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 to 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 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. Income Taxes For the three and nine months ended September 30, 2019, we recorded an income tax provision for our Nektar India operations at an effective tax rate of approximately 33%. Due to our net loss and unrealized gain on available-for-sale securities in the nine months ended September 30, 2019, we recorded a tax provision against such unrealized gain with an offsetting tax benefit in continuing operations of $1.3 million. For the three months ended September 30, 2019, however, since we had a loss on our available-for-sale securities, we recorded a benefit of $0.3 million against our unrealized loss in available-for-sale securities with an offsetting expense in continuing operations. We have fully reserved our U.S. federal deferred tax assets generated from our net operating losses, as we believe it is not more likely than not that the benefit will be realized. For the nine months ended September 30, 2018, as a result of taxable income in India and the U.S., resulting primarily from income recognized from the upfront payment from BMS, we recorded a global income tax provision at an effective tax rate of approximately 0.4%. The income tax benefit for the three months ended September 30, 2018 reflects our pre-tax loss for that period. Our income resulted in tax liabilities in certain states where we did not have sufficient net operating losses to offset our estimated apportioned taxable income. Our effective tax rate was based on certain assumptions and other estimates regarding the apportionment of taxable income and the states in which we had nexus in 2018. Our apportionment of taxable income included estimates of the apportionment of the BMS upfront payment based on estimates of activities to be carried out under the collaboration agreement with BMS, as well as estimates of the apportionment of other sources of income. Our effective tax rate reflected the release of the valuation allowance of net operating loss carryforwards and other tax credits to offset U.S. federal and state taxable income. Recent Accounting Pronouncements In November 2018, the Financial Accounting Standards Board (FASB) issued 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 effective in the first quarter of 2020 and should be applied retrospectively to January 1, 2018, when we adopted ASC 606. Early adoption is permitted. We are evaluating the effect of adoption, but we do not expect a material effect on our revenue. In June 2016, the FASB issued 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. Accordingly, we will present these financial assets 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 current, other-than-temporary-impairment model. ASU 2016-13 is effective in the first quarter of 2020. Early adoption is permitted. We are currently evaluating the impact of adoption of this ASU, but we do not anticipate that adoption will have a material effect on our Condensed Consolidated Financial Statements.

Cash and Investments in Marketable Securities

9 Months Ended

Sep. 30, 2019

Fair Value Disclosures [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
	September 30, 2019		December 31, 2018
Cash and cash equivalents	$	81,224	$	194,905
Short-term investments	1,414,448		1,140,445
Long-term investments	231,082		582,889
Total cash and investments in marketable securities	$	1,726,754	$	1,918,239

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. As of September 30, 2019 and December 31, 2018, all of our long-term investments had maturities between one and two years.

Gross unrealized gains and losses were not significant at either September 30, 2019 or December 31, 2018. During the three and nine months ended September 30, 2019 and the three months ended September 30, 2018, we sold no available-for-sale securities. During the nine months ended September 30, 2018, we sold available-for-sale securities totaling $12.0 million, and gross realized gains and losses on those 2018 sales were not significant. The cost of securities sold is based on the specific identification method.

Under the terms of our 7.75% senior secured notes due October 2020, we are required to maintain a minimum cash and investments in marketable securities balance of $60.0 million.

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



		Estimated Fair Value at
	Fair Value Hierarchy Level	September 30, 2019		December 31, 2018
Corporate notes and bonds	2	$	1,163,575	$	1,288,986
Corporate commercial paper	2	482,468		498,048
Obligations of U.S. government agencies	2	—		12,977
Available-for-sale investments		1,646,043		1,800,011
Money market funds	1	45,674		105,656
Certificate of deposit	N/A	6,871		6,760
Cash	N/A	28,166		5,812
Total cash and investments in marketable securities		$	1,726,754	$	1,918,239

____________________________


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.

During the three and nine months ended September 30, 2019 and 2018, 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.

Additionally, as of September 30, 2019, based on a discounted cash flow analysis using Level 3 inputs including financial discount rates, we believe the fair value of the $250.0 million in principal amount of our 7.75% senior secured notes due October 2020 is approximately $252.5 million. We may redeem some or all of these notes at a redemption price equal to the principal amount of the notes plus accrued and unpaid interest to the redemption date.

- 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

Leases

9 Months Ended

Sep. 30, 2019

Leases [Abstract]

Leases

In August 2017, we entered into a Lease Agreement (the Mission Bay Lease) with ARE-San Francisco No. 19, LLC (ARE) and terminated our sublease with Pfizer, Inc., effectively extending our lease term from 2020 to 2030 for our 145,085 square foot corporate office and R&D facility located at 455 Mission Bay Boulevard, San Francisco, California (the Mission Bay Facility). The term of the Mission Bay Lease commenced on September 1, 2017, and will expire on January 31, 2030, subject to our right to extend the term of the lease for two consecutive five-year periods, which we have excluded from our determination of the lease term. The monthly base rent for the Mission Bay Facility will escalate over the term of the lease at various intervals. 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 and taxes. The Mission Bay Lease also obligates us to rent from ARE a total of an additional approximately 8,000 square feet of space at the Mission Bay Facility. During the nine months ended September 30, 2019, ARE delivered 10,729 square feet of space, and therefore we recognized right-of-use assets and lease liabilities of $5.0 million for the space. The Mission Bay Lease includes various covenants, indemnities, defaults, termination rights, security deposits and other provisions customary for lease transactions of this nature.

In May 2018, we entered into a Lease Agreement (the Third Street Lease) with Kilroy Realty Finance Partnership, L.P. (Kilroy) to lease 135,936 square feet of space located at 360 Third Street, San Francisco, California (the Third Street Facility) from June 2018 to January 31, 2030, subject to our right to extend the term for a consecutive five-year period, which we have excluded from our determination of the lease term. Kilroy delivered an initial 1,726 square feet in June 2018, a total of 67,105 square feet for two additional spaces in December 2018, and the final 67,105 square feet for four spaces in August 2019. As a result of the delivery of the final spaces during the nine months ended September 30, 2019, we recognized an additional right-of-use asset and lease liability of $51.0 million. The Third Street Lease provides us additional facilities to support our San Francisco-based R&D activities. Our fixed monthly base rent on an industrial gross lease basis includes certain expenses and property taxes paid directly by the landlord and will escalate each year over the term at specified intervals. We have a one-time right of first offer with respect to certain additional rental space at the Third Street Facility. The Third Street Lease includes various covenants, indemnities, defaults, termination rights, security deposits and other provisions customary for lease transactions of this nature.

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



	Three months ended September 30,				Nine months ended September 30,
	2019		2018		2019		2018
Operating lease cost	$	4,116	$	1,927	$	10,030	$	5,651
Variable lease cost	1,485		1,096		4,539		3,371
Total lease costs	$	5,601	$	3,023	$	14,569	$	9,022

During the nine months ended September 30, 2019, we paid $5.1 million for amounts included in the measurement of lease liabilities, which we include in net cash provided by (used in) operating activities in our Condensed Consolidated Statement of Cash Flows.

As of September 30, 2019, the maturities of our operating lease liabilities were as follows (in thousands):



Year ended December 31,
2019 (Three months ended)	$	2,400
2020	15,283
2021	19,026
2022	19,633
2023	20,257
2024	20,899
2025 and thereafter	116,881
Total lease payments	214,379
Less: portion representing interest	(56,621		)
Less: lease incentives	(3,341		)
Operating lease liabilities	154,417
Less: current portion	(9,318		)
Operating lease liabilities, less current portion	$	145,099

As of September 30, 2019, the weighted-average remaining lease term is 10.3 years and the weighted-average discount rate used to determine the operating lease liability was 5.9%.

Liability Related to Sale of Future Royalties	9 Months Ended
Liability Related to Sale of Future Royalties	Sep. 30, 2019
Other Liabilities Disclosure [Abstract]
Liability Related to Sale of Future Royalties	Liability Related to Sale of Future Royalties On February 24, 2012, we entered into a Purchase and Sale Agreement (the 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 Royalty Entitlement) 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 Royalty Entitlement. As part of this sale, we incurred approximately $4.4 million in transaction costs, which are amortized to interest expense over the estimated life of the 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 (Royalty Obligation) that is amortized using the interest method over the estimated life of the Purchase and Sale Agreement as royalties from the CIMZIA^® and MIRCERA^® products are remitted directly to RPI. During the nine months ended September 30, 2019 and 2018, we recognized $27.6 million and $24.3 million, respectively, in non-cash royalty revenue from net sales of CIMZIA^® and MIRCERA^®, and we recorded $17.9 million and $14.8 million, respectively, of related non-cash interest expense. We periodically assess the estimated royalty payments to RPI from UCB and Roche, and, to the extent such payments are greater or less than our initial estimates or the timing of such payments is materially different from our original estimates, we will prospectively adjust the amortization of the Royalty Obligation. From inception through 2017, our estimate of the total interest expense on the Royalty Obligation resulted in an effective annual interest rate of approximately 17%. During the three months ended December 31, 2017, our estimate of the effective annual interest rate over the life of the agreement increased to 17.6%, which resulted in a prospective interest rate of approximately 21%. During the three months ended December 31, 2018, primarily as a result of increases in the forecasted sales of MIRCERA^®, our estimate of the effective annual interest rate over the life of the agreement increased to 18.7%, which results in a prospective interest rate of 29%. The Purchase and Sale Agreement grants RPI the right to receive certain reports and other information relating to the Royalty Entitlement and contains other representations and warranties, covenants and indemnification obligations that are customary for a transaction of this nature. To our knowledge, we are currently in compliance with these provisions of the Purchase and Sale Agreement; however, if we were to breach our obligations, we could be required to pay damages to RPI that are not limited to the purchase price we received in the sale transaction.

Commitments and Contingencies	9 Months Ended
Commitments and Contingencies	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies 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, 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 Nektar’s board. Both the 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 NKTR-214. In addition, on August 19, 2019, 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, which complaint asserted, 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 NKTR-214 manufacturing issue. All of these cases are in the early stages. Accordingly, we cannot reasonably estimate any range of potential future charges, and we have not recorded any accrual for a contingent liability associated with these legal proceedings. 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. 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 obligation to RPI described in Note 5. In the event it is determined that we breached certain of the representations and warranties or covenants made by us in any such agreements, 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 Condensed Consolidated Balance Sheets at either September 30, 2019 or December 31, 2018.

License and Collaboration Agreements

9 Months Ended

Sep. 30, 2019

Organization, Consolidation and Presentation of Financial Statements [Abstract]

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. Our partners may generally cancel our collaboration agreements without significant financial penalty. 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):



		Three months ended September 30,				Nine months ended September 30,
Partner	Drug or Drug Candidate	2019		2018		2019		2018
Bristol-Myers Squibb Company	NKTR-214	$	—	$	—	$	—	$	1,059,768
Eli Lilly and Company	NKTR-358	1,500		3,221		5,200		8,627
Amgen, Inc.	Neulasta^®	1,250		1,250		3,750		3,750
Baxalta Inc. / Takeda Pharmaceutical Company Ltd. and other	ADYNOVATE^®	371		404		910		10,703
License, collaboration and other revenue		$	3,121	$	4,875	9,860		$	1,082,848

In the three and nine months ended September 30, 2019, we recognized $20.5 million and $56.6 million of revenue for performance obligations that we had satisfied in prior periods, respectively. This amount includes all of our royalty revenue and non-cash royalty revenue because these royalties substantially relate to the licenses that we had previously granted.

In the three and nine months ended September 30, 2018, we recognized $18.6 million and $64.2 million of revenue for performance obligations that we had satisfied in prior periods. This amount includes all of our royalty revenue and non-cash royalty revenue because these royalties substantially relate to the licenses that we had previously granted. This amount also includes the $10.0 million development milestone payment earned and received from Baxalta Inc. in the nine months ended September 30, 2018 described below.

The following table presents the changes in our deferred revenue balance from our collaboration agreements during the nine months ended September 30, 2019 (in thousands):



	Nine months ended September 30, 2019
Deferred revenue—December 31, 2018	$	24,636
Recognition of previously unearned revenue	(9,465		)
Deferred revenue—September 30, 2019	$	15,171

Our balance of deferred revenue contains the transaction price from our collaboration agreements allocated to performance obligations which are partially unsatisfied. We expect to recognize approximately $8.4 million of our deferred revenue over the next twelve months and recognize the remaining $6.8 million over several years.

As of September 30, 2019, our collaboration agreements with partners included potential future payments for development and regulatory 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 contingent sales milestone payments, other contingent payments and royalty payments, as described below.

There have been no material changes to our collaboration agreements in the three and nine months ended September 30, 2019, except as described below.

Bristol-Myers Squibb Company (BMS): Bempegaldesleukin, also referred to as NKTR-214

On February 13, 2018, we entered into a Strategic Collaboration Agreement (BMS Collaboration Agreement) and a Share Purchase Agreement with BMS, both of which became effective on April 3, 2018. Pursuant to these agreements, we and BMS are

jointly developing NKTR-214, including, without limitation, in combination with BMS’s Opdivo^® (nivolumab) and Opdivo^® plus Yervoy^® (ipilimumab), and other compounds of BMS, us or any third party. The parties have agreed to jointly commercialize NKTR-214 on a worldwide basis. We retained the right to record all worldwide sales for NKTR-214. We will share global commercialization profits and losses with BMS for NKTR-214, with Nektar sharing 65% and BMS sharing 35% of the net profits and losses. The parties will share the internal and external development costs for NKTR-214 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 will share development costs for NKTR-214 in combination with Opdivo^®, 67.5% of costs to BMS and 32.5% to Nektar, and for NKTR-214 in a triplet combination with Opdivo^® and Yervoy^®, 78% of costs to BMS and 22% to Nektar. The parties will share costs for the manufacturing of NKTR-214, 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 NKTR-214 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 $1.4 billion 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.

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 costs as a reduction of research and development expense and our reimbursement of BMS’ costs as research and development expense. During the three and nine months ended September 30, 2019, we recorded $28.3 million and $81.4 million, respectively, as a reduction of research and development expense for BMS’ share of our expenses, net of our share of BMS’ expenses. During the three and nine months ended September 30, 2018, we recorded $18.9 million and $42.8 million, respectively, as a reduction of research and development expense for BMS’ share of our expenses, net of our share of BMS’ expenses. As of September 30, 2019, we have recorded a receivable of $27.7 million from BMS in accounts receivable in our Condensed Consolidated Balance Sheet.

We analogized to ASC 606 for the accounting for our two performance obligations, consisting of the delivery of the licenses to develop and commercialize NKTR-214 and our participation on joint steering and other collaboration committees. We determined that our committee participation is not material.

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 based on the closing date price of our common stock of $99.36, adjusted for a discount for lack of marketability reflecting the unregistered nature of the shares. We allocated the remaining $1,059.8 million to the transaction price of the collaboration agreement. We consider the future potential development, regulatory and sales milestones of up to approximately $1.8 billion to be variable consideration. We excluded these milestones from the transaction price during 2018 and as of September 30, 2019 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.

Accordingly, we allocated the entire transaction price of $1,059.8 million to the granting of the licenses and therefore recognized $1,059.8 million during the nine months ended September 30, 2018 as license, collaboration and other revenue.

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 are responsible for completing

Phase 1 clinical development and certain drug product development and supply activities, (iii) will share with Lilly Phase 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 up to double-digit sales royalty rates that escalate 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 ongoing 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 September 30, 2019, 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 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 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 recognize revenue for 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 September 30, 2019, we have deferred revenue of approximately $3.1 million related to this agreement, which we expect to recognize through early 2020, the estimated end of our performance obligations under this agreement.

Baxalta Inc. / Takeda Pharmaceutical Company Ltd: 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 United States Food and Drug Administration (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. We updated the transaction price for this milestone in January 2018 since we had previously excluded it due to the significant uncertainty from regulatory approval. Based on the terms of this milestone, we allocated the entire milestone to the license grant and research and development services, and therefore recognized the entire $10.0 million in the nine months ended September 30, 2018 as we had previously satisfied those performance obligations. In December 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 September 30, 2019, our deferred revenue from this arrangement 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 Amended and Restated Agreement) and a license agreement with Amgen, Inc. and Amgen Manufacturing, Limited (together referred to as Amgen). Under the terms of the Amended and Restated 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 our PEGylation materials and to maintain the dedicated manufacturing suite solely for the production of such materials for Amgen 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. As of September 30, 2019, we have deferred revenue of approximately $5.4 million related to this agreement, which we expect to recognize through October 2020, the estimated end of our obligations under this agreement.

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 September 30, 2019, 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 will 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 September 30, 2019, 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 opioid-induced constipation 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 of September 30, 2019, our cumulative share of the post-approval study expenses since 2015 totaled $1.7 million. AstraZeneca may only recover costs incurred by the reduction of the royalty payable to us. 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.

Other

In addition, as of September 30, 2019, we have a number of other collaboration agreements, including with our collaboration partners UCB Pharma and Halozyme Therapeutics, Inc., under which we are entitled to up to a total of $45.5 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 September 30, 2019, we have deferred revenue of approximately $6.0 million related to these other collaboration agreements.

Organization and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
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 treatments for cancer, autoimmune disease and chronic pain. 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 and Principles of Consolidation	Basis of Presentation and Principles of Consolidation Our consolidated financial statements include the financial position, results of operations and cash flows of our wholly-owned subsidiaries: Inheris Biopharma, Inc., Nektar Therapeutics (India) Private Limited (Nektar India) and Nektar Therapeutics UK Limited. We have eliminated all intercompany accounts and transactions in consolidation. We prepared our Condensed Consolidated Financial Statements following the requirements of the Securities and Exchange Commission (SEC) for interim reporting. As permitted under those rules, we may condense or omit certain footnotes or other financial information that are normally required by U.S. generally accepted accounting principles (GAAP) for annual periods. In the opinion of management, these financial statements include all normal and recurring adjustments that we consider necessary for the fair presentation of our financial position and operating results. Our Condensed 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 Condensed 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, neither of which were significant during the three and nine months ended September 30, 2019 and 2018. In addition, there were no significant reclassifications out of accumulated other comprehensive loss to the statements of operations during the three and nine months ended September 30, 2019 and 2018. The accompanying Condensed Consolidated Financial Statements are unaudited. The Condensed Consolidated Balance Sheet data as of December 31, 2018 was derived from the audited consolidated financial statements which are included in our Annual Report on Form 10-K for the year ended December 31, 2018 filed with the SEC on March 1, 2019. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the consolidated financial statements and the accompanying notes to those financial statements included in our Annual Report on Form 10-K for the year ended December 31, 2018. Revenue, expenses, assets, and liabilities can vary during each quarter of the year. The results and trends in these interim Condensed Consolidated Financial Statements are not necessarily indicative of the results to be expected for the full year or any other period.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with 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. As appropriate, we assess our estimates each period, update them to reflect current information and generally recognize any changes in such estimates in the period first identified.
Segment Information	Segment Information We operate in one business segment which focuses on applying our technology platform 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.
Significant Concentrations	Significant Concentrations Our customers are primarily pharmaceutical and biotechnology companies that are 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, other contingent payments and royalties, as well as reimbursable costs from collaborative research and development agreements. As of September 30, 2019 and December 31, 2018, our accounts receivable includes $27.7 million and $24.2 million, respectively, for net expense reimbursements from our collaboration partner Bristol-Myers Squibb Company (BMS). 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, our ability to develop and produce our drug candidates 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 three and nine months ended September 30, 2019 under ASC 842. We have not restated the results for the three and nine months ended September 30, 2018 and our financial position as of December 31, 2018, and 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 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 real estate 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.
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. 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, we are entitled to royalties from our collaboration partners based on the net sales of their approved drugs that are marketed and sold in one or more countries where we hold royalty rights. For arrangements that include sales-based royalties, including commercial milestone payments based on the level of sales, we have concluded that the license is the predominant item to which the royalties relate. 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 or filing for or receipt of regulatory approval, 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. 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.
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 clinical 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 our 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 to 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 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.
Income Taxes	Income Taxes For the three and nine months ended September 30, 2019, we recorded an income tax provision for our Nektar India operations at an effective tax rate of approximately 33%. Due to our net loss and unrealized gain on available-for-sale securities in the nine months ended September 30, 2019, we recorded a tax provision against such unrealized gain with an offsetting tax benefit in continuing operations of $1.3 million. For the three months ended September 30, 2019, however, since we had a loss on our available-for-sale securities, we recorded a benefit of $0.3 million against our unrealized loss in available-for-sale securities with an offsetting expense in continuing operations. We have fully reserved our U.S. federal deferred tax assets generated from our net operating losses, as we believe it is not more likely than not that the benefit will be realized.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In November 2018, the Financial Accounting Standards Board (FASB) issued 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 effective in the first quarter of 2020 and should be applied retrospectively to January 1, 2018, when we adopted ASC 606. Early adoption is permitted. We are evaluating the effect of adoption, but we do not expect a material effect on our revenue. In June 2016, the FASB issued 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. Accordingly, we will present these financial assets 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 current, other-than-temporary-impairment model. ASU 2016-13 is effective in the first quarter of 2020. Early adoption is permitted. We are currently evaluating the impact of adoption of this ASU, but we do not anticipate that adoption will have a material effect on our Condensed Consolidated Financial Statements.
Inventory	nventory 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 as manufactured by us or when purchased.
Liability Related to Sale of Future Royalties	We periodically assess the estimated royalty payments to RPI from UCB and Roche, and, to the extent such payments are greater or less than our initial estimates or the timing of such payments is materially different from our original estimates, we will prospectively adjust the amortization of the Royalty Obligation.

Cash and Investments in Marketable Securities (Tables)

9 Months Ended

Sep. 30, 2019

Fair Value Disclosures [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
	September 30, 2019		December 31, 2018
Cash and cash equivalents	$	81,224	$	194,905
Short-term investments	1,414,448		1,140,445
Long-term investments	231,082		582,889
Total cash and investments in marketable securities	$	1,726,754	$	1,918,239

Portfolio of Cash and Investments in Marketable Securities

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



		Estimated Fair Value at
	Fair Value Hierarchy Level	September 30, 2019		December 31, 2018
Corporate notes and bonds	2	$	1,163,575	$	1,288,986
Corporate commercial paper	2	482,468		498,048
Obligations of U.S. government agencies	2	—		12,977
Available-for-sale investments		1,646,043		1,800,011
Money market funds	1	45,674		105,656
Certificate of deposit	N/A	6,871		6,760
Cash	N/A	28,166		5,812
Total cash and investments in marketable securities		$	1,726,754	$	1,918,239

License and Collaboration Agreements (Tables)

9 Months Ended

Sep. 30, 2019

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):



		Three months ended September 30,				Nine months ended September 30,
Partner	Drug or Drug Candidate	2019		2018		2019		2018
Bristol-Myers Squibb Company	NKTR-214	$	—	$	—	$	—	$	1,059,768
Eli Lilly and Company	NKTR-358	1,500		3,221		5,200		8,627
Amgen, Inc.	Neulasta^®	1,250		1,250		3,750		3,750
Baxalta Inc. / Takeda Pharmaceutical Company Ltd. and other	ADYNOVATE^®	371		404		910		10,703
License, collaboration and other revenue		$	3,121	$	4,875	9,860		$	1,082,848

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 nine months ended September 30, 2019 (in thousands):



	Nine months ended September 30, 2019
Deferred revenue—December 31, 2018	$	24,636
Recognition of previously unearned revenue	(9,465		)
Deferred revenue—September 30, 2019	$	15,171

Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2019

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock-Based Compensation Expense

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



	Three months ended September 30,				Nine months ended September 30,
	2019		2018		2019		2018
Cost of goods sold	$	1,119	$	1,176	$	3,208	$	3,470
Research and development	15,680		15,365		47,549		40,449
General and administrative	8,081		6,746		24,030		19,976
Total stock-based compensation	$	24,880	$	23,287	$	74,787	$	63,895

Share-based Compensation, Activity

We issued stock-based awards and resulting shares of our common stock as follows (shares in thousands):



	Three months ended September 30,				Nine months ended September 30,
	2019		2018		2019		2018
Options granted	131		190		246		929
Weighted-average grant-date fair value of options granted	$	13.43	$	30.52	$	15.81	$	39.28
RSUs granted	316		152		712		558
Weighted-average grant-date fair value of RSUs granted	$	28.00	$	57.27	$	31.80	$	54.49
Shares issued under equity compensation plans	820		642		2,256		5,248

Organization and Summary of Significant Accounting Policies - Additional Information (Detail)		3 Months Ended		9 Months Ended
	Jan. 01, 2019 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2019 USD ($) Segment	Sep. 30, 2018	Dec. 31, 2018 USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items]
Cash and investments in marketable securities		$ 1,726,754,000		$ 1,726,754,000		$ 1,918,239,000
Senior secured notes		250,000,000.0		$ 250,000,000.0
Number of business segment \| Segment				1
Accounts receivable for expense reimbursements from collaboration partner		41,205,000		$ 41,205,000		43,213,000
Operating lease, right-of-use assets		134,888,000		134,888,000		0
Operating lease, lease liabilities		154,417,000		154,417,000
Cumulative effect adjustment to accumulated deficit			$ 12,577,000
Effective income tax rate					0.40%
Tax provision on unrealized gain on available-for-sale securities, offset by benefit in continuing operations		$ 300,000		$ 1,300,000
India
Organization And Summary Of Significant Accounting Policies [Line Items]
Effective income tax rate		33.00%		33.00%
ASC 842
Organization And Summary Of Significant Accounting Policies [Line Items]
Operating lease, right-of-use assets	$ 83,500,000
Operating lease, lease liabilities	96,200,000
Cumulative effect adjustment to accumulated deficit	$ 0
Collaboration Partner
Organization And Summary Of Significant Accounting Policies [Line Items]
Accounts receivable for expense reimbursements from collaboration partner		$ 27,700,000		$ 27,700,000		$ 24,200,000

Cash and Investments in Marketable Securities - Cash and Investments in Marketable Securities, Including Cash Equivalents (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	$ 81,224	$ 194,905
Short-term investments	1,414,448	1,140,445
Long-term investments	231,082	582,889
Total cash and investments in marketable securities	$ 1,726,754	$ 1,918,239

Cash and Investments in Marketable Securities - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Oct. 05, 2015
Cash and Investments in Marketable Securities [Line Items]
Maximum maturity term for debt securities investment			2 years
Weighted average maturity term for debt securities investment (or less)			1 year
Available-for-sale securities, sold	$ 0	$ 0	$ 0	$ 11,963,000
Level 1 to level 2 transfers	0	0	0	0
Level 2 to level 1 transfers	0	$ 0	0	$ 0
Senior secured notes, principal amount	$ 250,000,000.0		$ 250,000,000.0
Senior Notes \| 7.75% Senior Secured Notes Due October 2020
Cash and Investments in Marketable Securities [Line Items]
Senior secured notes, interest rate						7.75%
Minimum cash and investments in marketable securities to be maintained						$ 60,000,000.0
Senior Notes \| 7.75% Senior Secured Notes Due October 2020 \| Level 3
Cash and Investments in Marketable Securities [Line Items]
Senior secured notes, interest rate	7.75%		7.75%
Senior secured notes, principal amount	$ 250,000,000.0		$ 250,000,000.0
Senior notes, fair value	$ 252,500,000		$ 252,500,000
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	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	$ 1,646,043	$ 1,800,011
Cash	28,166	5,812
Total cash and investments in marketable securities	1,726,754	1,918,239
Corporate Notes and Bonds \| Fair Value Hierarchy Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	1,163,575	1,288,986
Corporate Commercial Paper \| Fair Value Hierarchy Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	482,468	498,048
Obligations of U.S. Government Agencies \| Fair Value Hierarchy Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	0	12,977
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	45,674	105,656
Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	$ 6,871	$ 6,760

Inventory - Inventory (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 1,586	$ 1,846
Work-in-process	7,961	6,403
Finished goods	4,173	3,132
Total inventory	$ 13,720	$ 11,381

Leases - Additional Information (Detail) $ in Thousands	1 Months Ended		9 Months Ended
Leases - Additional Information (Detail) $ in Thousands	Dec. 31, 2018 ft² space	Aug. 31, 2017 ft² extension_period	Sep. 30, 2019 USD ($) ft²	Sep. 30, 2018 USD ($)	Aug. 31, 2019 ft²	Jun. 30, 2018 ft²	May 31, 2018 ft²
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets recognized in exchange for lease liabilities			$ 56,025	$ 0
Cash paid for amounts included in the measurement of lease liabilities			$ 5,100
Operating lease liability, weighted-average remaining lease term			10 years 3 months 18 days
Operating lease liability, weighted-average discount rate, percent			5.90%
ARE-San Francisco No. 19, LLC \| Mission Bay Lease
Lessee, Lease, Description [Line Items]
Lease space (in sq. feet) \| ft²		145,085	10,729
Number of consecutive 5 year terms to extend lease \| extension_period		2
Lease extension term		5 years
Additional space required to be leased in the future (in sqft) \| ft²		8,000
Operating lease right-of-use assets recognized in exchange for lease liabilities			$ 5,000
Kilroy Realty Finance Partnership, L.P \| Third Street Lease
Lessee, Lease, Description [Line Items]
Lease space (in sq. feet) \| ft²	67,105				67,105	1,726	135,936
Lease extension term							5 years
Operating lease right-of-use assets recognized in exchange for lease liabilities			$ 51,000
Number of additional spaces delivered \| space	2

Leases - Components of Lease Costs Included in Operating Expenses (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Leases [Abstract]
Operating lease cost	$ 4,116	$ 1,927	$ 10,030	$ 5,651
Variable lease cost	1,485	1,096	4,539	3,371
Total lease costs	$ 5,601	$ 3,023	$ 14,569	$ 9,022

Leases - Summary of Maturities of Operating Lease Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Leases [Abstract]
2019 (three months ended)	$ 2,400
2020	15,283
2021	19,026
2022	19,633
2023	20,257
2024	20,899
2025 and thereafter	116,881
Total lease payments	214,379
Less: portion representing interest	(56,621)
Less: lease incentives	(3,341)
Operating lease liabilities	154,417
Less: current portion	(9,318)	$ 0
Operating lease liabilities, less current portion	$ 145,099	$ 0

Liability Related to Sale of Future Royalties - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended		70 Months Ended
	Feb. 24, 2012	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
Liability Related to Sale of Future Royalties [Line Items]
Non-cash royalty revenue related to sale of future royalties						$ 27,585	$ 24,337
Non-cash interest expense on liability related to sale of future royalties		$ (5,813)		$ (4,814)		$ (17,853)	$ (14,808)
Annual interest rate			18.70%		17.60%			17.00%
Prospective interest rate			29.00%		21.00%
Purchase and Sale Agreement with RPI
Liability Related to 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

License and Collaboration Agreements - Additional Information (Detail) - USD ($)			1 Months Ended								3 Months Ended			9 Months Ended		76 Months Ended
	Feb. 13, 2018	Aug. 23, 2017	Dec. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Nov. 30, 2017	Sep. 30, 2017	Aug. 31, 2017	Sep. 30, 2016	Mar. 31, 2016	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2010	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2015
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized in period related to performance in prior periods											$ 20,500,000	$ 18,600,000		$ 56,600,000	$ 64,200,000
Deferred revenue, current portion			$ 13,892,000								8,392,000			8,392,000
Deferred revenue, less current portion			10,744,000								6,779,000			6,779,000
Potential future additional development and regulatory milestones											1,700,000,000			1,700,000,000
Accounts receivable			43,213,000								41,205,000			41,205,000
Revenue recognized from contracts with customers											29,218,000	27,762,000		80,755,000	1,153,497,000
Deferred revenue			24,636,000								15,171,000			15,171,000
NKTR-358 \| Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue											3,100,000			3,100,000
BMS Collaboration Agreement \| NKTR-214 \| Nektar's
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront and milestone payments received from license agreements				$ 1,000,000,000.0
Global commercialization profits and losses sharing percentage	65.00%
Percentage of sharing production costs	65.00%
Maximum total additional cash payments receivable upon achievement of certain development and regulatory milestones				1,400,000,000
BMS Collaboration Agreement \| NKTR-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
BMS Collaboration Agreement \| NKTR-214 \| Nektar's \| Opdivo
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	32.50%
BMS Collaboration Agreement \| NKTR-214 \| Nektar's \| Opdivo and Yervoy
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	22.00%
NKTR-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%
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]
Upfront and milestone payments received from license agreements															10,000,000.0
Revenue recognized from contracts with customers					$ 10,000,000.0										10,000,000.0
Bristol-Myers Squibb Company \| Purchase Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Shares issued (in shares)				8,284,600
Sale of stock consideration received				$ 850,000,000.0
Bristol-Myers Squibb Company \| NKTR-214 \| Research and Development Expense
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Reimbursement of expenses											28,300,000	$ 18,900,000		81,400,000	42,800,000
Bristol-Myers Squibb Company \| BMS Collaboration Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Accounts receivable											27,700,000			27,700,000
Bristol-Myers Squibb Company \| BMS 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
Closing date price of common stock (in dollars per share)				$ 99.36
Remaining amount allocated to transaction price				$ 1,059,800,000
Potential future development, regulatory and sales milestones				$ 1,800,000,000
Bristol-Myers Squibb Company \| BMS Collaboration Agreement \| NKTR-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%
Amount recognized for granting licenses															$ 1,059,800,000
Bristol-Myers Squibb Company \| BMS Collaboration Agreement \| NKTR-214 \| Opdivo
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	67.50%
Bristol-Myers Squibb Company \| BMS Collaboration Agreement \| NKTR-214 \| Opdivo and Yervoy
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	78.00%
Bristol-Myers Squibb Company \| Clinical Trial Agreement \| NKTR-214
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of out-of-pocket costs to be reimbursed by partner									50.00%
Eli Lilly and Company \| NKTR-358 \| ASC 606
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenue recognized from contracts with customers								$ 125,900,000
Eli Lilly and Company \| NKTR-358 License
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount of transaction price allocated to performance obligation							125,900,000
Eli Lilly and Company \| NKTR-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 \| NKTR-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 \| NKTR-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 \| NKTR-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 \| NKTR-358 License
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 \| NKTR-358 License
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Amount of transaction price allocated to performance obligation							$ 6,500,000
Eli Lilly \| NKTR-358
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Percentage of sharing in Phase 2 development costs		75.00%
Amgen, Inc.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment													$ 50,000,000.0
Amgen, Inc. \| ASC 606
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue											5,400,000			$ 5,400,000
AstraZeneca AB \| MOVANTIK and MOVENTIG
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment																$ 385,000,000.0
Amount of post approval study expenses eligible for reimbursement														33.00%
Amount of post approval study expenses eligible for reimbursement, maximum														$ 35,000,000.0
Share of expenses														1,700,000
AstraZeneca 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%
Baxalta Inc. / Takeda Pharmaceutical Company Ltd. and other
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue											6,000,000.0			6,000,000.0
Potential future additional payments for development milestones											$ 45,500,000			$ 45,500,000

Stock-Based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 24,880	$ 23,287	$ 74,787	$ 63,895
Cost of goods sold
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	1,119	1,176	3,208	3,470
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	15,680	15,365	47,549	40,449
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 8,081	$ 6,746	$ 24,030	$ 19,976

Stock-Based Compensation - Activity (Detail) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares issued under equity compensation plans (in shares)	820,000	642,000	2,256,000	5,248,000
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted stock options (in shares)	131,000	190,000	246,000	929,000
Weighted average grant-date fair value, options (in dollars per share)	$ 13.43	$ 30.52	$ 15.81	$ 39.28
Restricted Stock Units (RSU)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)	316,000	152,000	712,000	558,000
Weighted average grant-date fair value, RSUs (in dollars per share)	$ 28.00	$ 57.27	$ 31.80	$ 54.49

Net Income (Loss) Per Share - Additional Information (Detail) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average antidilutive securities excluded from computation of earnings per share (in shares)		17.6		3.2
Weighted average potentially dilutive securities included in calculation of diluted securities (in shares)				11.3
Stock Options and Restricted Stock Units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Weighted average antidilutive securities excluded from computation of earnings per share (in shares)	17.2		18.0

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Comprehensive income (loss)	$ (99,206)	$ (97,519)	$ (322,099)	$ 776,258

Net Income (Loss) Per Share	9 Months Ended
Net Income (Loss) Per Share	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	Net Income (Loss) Per Share 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. For all periods presented in the accompanying Condensed Consolidated Statements of Operations, our net income (loss) available to common stockholders equals the reported net income (loss). For the three and nine months ended September 30, 2019 and the three months ended September 30, 2018, 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. During the three and nine months ended September 30, 2019 and the three months ended September 30, 2018, potentially dilutive securities consisted of the weighted-average common shares underlying outstanding stock options and RSUs, which totaled 17.2 million, 18.0 million and 17.6 million shares, respectively. For the computation of diluted earnings per share for nine months ended September 30, 2018, we included approximately 11.3 million weighted-average common shares underlying stock options and RSUs under the treasury stock method and excluded approximately 3.2 million of shares of common stock underlying stock options because their effect was antidilutive.

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Sep. 30, 2019	Dec. 31, 2018
Indemnification Obligation
Loss Contingencies [Line Items]
Litigation matters, liabilities	$ 0	$ 0

License and Collaboration Agreements - Changes in Deferred Revenue Balance from Collaboration Agreements (Detail) $ in Thousands	9 Months Ended
	Sep. 30, 2019 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Deferred revenue, Beginning balance	$ 24,636
Recognition of previously unearned revenue	(9,465)
Deferred revenue, Ending balance	$ 15,171