Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2018	Feb. 22, 2019	Jun. 29, 2018
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Trading Symbol	NKTR
Entity Registrant Name	NEKTAR THERAPEUTICS
Entity Central Index Key	0000906709
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		174,104,459
Entity Public Float			$ 8,366,439,130

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 194,905	$ 4,762
Short-term investments	1,140,445	291,370
Accounts receivable	43,213	5,014
Inventory	11,381	10,726
Advance payments to contract manufacturers	26,450	7,155
Other current assets	21,293	7,793
Total current assets	1,437,687	326,820
Long-term investments	582,889	57,088
Property, plant and equipment, net	48,851	47,463
Goodwill	76,501	76,501
Other assets	4,244	994
Total assets	2,150,172	508,866
Current liabilities:
Accounts payable	5,854	4,782
Accrued compensation	9,937	8,263
Accrued contract manufacturing expenses	23,841	3,845
Accrued clinical trial expenses	14,700	9,461
Other accrued expenses	9,087	6,219
Interest payable	4,198	4,198
Deferred revenue, current portion	13,892	18,949
Other current liabilities	493	446
Total current liabilities	82,002	56,163
Senior secured notes, net	246,950	245,207
Liability related to the sale of future royalties, net	82,911	94,655
Deferred revenue, less current portion	10,744	19,021
Other long-term liabilities	9,990	5,992
Total liabilities	432,597	421,038
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares designated, issued or outstanding at December 31, 2018 or 2017	0	0
Common stock, $0.0001 par value; 300,000 shares authorized; 173,530 shares and 159,524 shares issued and outstanding at December 31, 2018 and 2017, respectively	17	15
Capital in excess of par value	3,147,925	2,207,865
Accumulated other comprehensive loss	(6,316)	(2,111)
Accumulated deficit	(1,424,051)	(2,117,941)
Total stockholders’ equity	1,717,575	87,828
Total liabilities and stockholders’ equity	$ 2,150,172	$ 508,866

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares designated	0	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	173,530,000	159,524,000
Common stock, shares outstanding	173,530,000	159,524,000

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue:
Total revenue	$ 1,193,323	$ 307,711	$ 165,436
Operating costs and expenses:
Cost of goods sold	$ 24,412	$ 30,547	$ 30,215
Type of Cost, Good or Service [Extensible List]	us-gaap:ProductMember	us-gaap:ProductMember	us-gaap:ProductMember
Research and development	$ 399,536	$ 268,461	$ 203,801
General and administrative	81,443	52,364	44,275
Impairment of equipment and other costs for terminated program	0	15,981	0
Total operating costs and expenses	505,391	367,353	278,291
Income (loss) from operations	687,932	(59,642)	(112,855)
Non-operating income (expense):
Interest expense	(21,582)	(22,085)	(22,468)
Non-cash interest expense on liability related to sale of future royalties	(21,196)	(18,869)	(19,712)
Interest income and other income (expense), net	37,571	4,520	2,387
Total non-operating expense, net	(5,207)	(36,434)	(39,793)
Income (loss) before provision for income taxes	682,725	(96,076)	(152,648)
Provision for income taxes	1,412	616	876
Net income (loss)	$ 681,313	$ (96,692)	$ (153,524)
Net income (loss) per share
Basic	$ 4.02	$ (0.62)	$ (1.10)
Diluted	$ 3.78	$ (0.62)	$ (1.10)
Weighted average shares outstanding used in computing net income (loss) per share
Basic	169,600	155,953	139,596
Diluted	180,119	155,953	139,596
Product Sales [Member]
Revenue:
Total revenue	$ 20,774	$ 32,688	$ 55,354
Royalty Revenue [Member]
Revenue:
Total revenue	41,976	33,527	19,542
Non-cash Royalty Revenue Related to Sale of Future Royalties [Member]
Revenue:
Total revenue	33,308	30,531	30,158
License, Collaboration and Other Revenue [Member]
Revenue:
Total revenue	$ 1,097,265	$ 210,965	$ 60,382

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income (loss)	$ 681,313	$ (96,692)	$ (153,524)
Other comprehensive income (loss):
Net unrealized gain (loss) on available-for-sale investments, net of tax	(2,975)	(533)	79
Net foreign currency translation gain (loss)	(1,230)	785	(272)
Other comprehensive income (loss), net of tax	(4,205)	252	(193)
Comprehensive income (loss)	$ 677,108	$ (96,440)	$ (153,717)

- Definition

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

+ References + Details

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Bristol-Myers Squibb [Member]	Common Shares [Member]	Common Shares [Member] Bristol-Myers Squibb [Member]	Capital in Excess of Par Value [Member]	Capital in Excess of Par Value [Member] Bristol-Myers Squibb [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]	Accumulated Other Comprehensive Income/(Loss) [Member] Bristol-Myers Squibb [Member]	Accumulated Deficit [Member]	Accumulated Deficit [Member] Bristol-Myers Squibb [Member]
Beginning Balance at Dec. 31, 2015	$ 6,429		$ 13		$ 1,876,072		$ (2,170)		$ (1,867,486)
Beginning Balance, Shares at Dec. 31, 2015			135,289
Sale of stock	189,276		$ 2		189,274		0		0
Sale of stock, Shares			14,950
Shares issued under equity compensation plans	20,287		$ 0		20,287		0		0
Shares issued under equity compensation plans, Shares			2,973
Stock-based compensation	25,850		$ 0		25,850		0		0
Other comprehensive loss	(193)		0		0		(193)		0
Net loss	(153,524)		0		0		0		(153,524)
Ending Balance at Dec. 31, 2016	88,125		$ 15		2,111,483		(2,363)		(2,021,010)
Ending Balance, Shares at Dec. 31, 2016			153,212
Shares issued under equity compensation plans	59,528		$ 0		59,528		0		0
Shares issued under equity compensation plans, Shares			6,312
Stock-based compensation	36,615		$ 0		36,615		0		0
Other comprehensive loss	252		0		239		252		(239)
Net loss	(96,692)		0		0		0		(96,692)
Ending Balance at Dec. 31, 2017	87,828		$ 15		2,207,865		(2,111)		(2,117,941)
Ending Balance, Shares at Dec. 31, 2017			159,524
Sale of stock		$ 790,232		$ 1		$ 790,231		$ 0		$ 0
Sale of stock, Shares				8,285
Shares issued under equity compensation plans	61,729		$ 1		61,728		0		0
Shares issued under equity compensation plans, Shares			5,721
Stock-based compensation	88,101		$ 0		88,101		0		0
Adoption of new accounting standards	12,577		0		0		0		12,577
Other comprehensive loss	(4,205)		0		0		(4,205)		0
Net loss	681,313		0		0		0		681,313
Ending Balance at Dec. 31, 2018	$ 1,717,575		$ 17		$ 3,147,925		$ (6,316)		$ (1,424,051)
Ending Balance, Shares at Dec. 31, 2018			173,530

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended			82 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Cash flows from operating activities:
Net income (loss)	$ 681,313	$ (96,692)	$ (153,524)
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	(33,308)	(30,531)	(30,158)	$ (170,839)
Non-cash interest expense on liability related to sale of future royalties	21,196	18,869	19,712	141,649
Stock-based compensation	88,101	36,615	25,850
Depreciation and amortization	10,870	14,741	15,351
Impairment of equipment from terminated program	0	15,081	0
Accretion of discounts, net, and other non-cash transactions	(10,952)	(881)	(2,185)
Changes in operating assets and liabilities:
Accounts receivable	(25,505)	10,664	4,269
Inventory	(655)	383	237
Other assets	(31,652)	(4,800)	(312)
Accounts payable	971	2,074	518
Accrued compensation	1,674	(10,017)	12,282
Other accrued expenses	27,947	7,277	(71)
Deferred revenue	(15,331)	(28,269)	(17,615)
Other liabilities	3,545	(14,928)	8,622
Net cash provided by (used in) operating activities	718,214	(80,414)	(117,024)
Cash flows from investing activities:
Purchases of investments	(2,271,250)	(404,425)	(334,659)
Maturities of investments	890,957	347,743	253,682
Sales of investments	11,963	37,549	4,969
Purchases of property, plant and equipment	(14,239)	(9,676)	(6,392)
Sales of property and plant	2,633	0	0
Net cash used in investing activities	(1,379,936)	(28,809)	(82,400)
Cash flows from financing activities:
Payment of capital lease obligations	0	(5,131)	(5,945)
Proceeds from shares issued under equity compensation plans	61,735	59,522	20,287
Issuance of common stock, net of issuance costs	790,231	0	189,276
Net cash provided by financing activities	851,966	54,391	203,618
Effect of exchange rates on cash and cash equivalents	(101)	(46)	(124)
Net increase (decrease) in cash and cash equivalents	190,143	(54,878)	4,070
Cash and cash equivalents at beginning of year	4,762	59,640	55,570
Cash and cash equivalents at end of year	194,905	4,762	59,640	$ 194,905
Supplemental disclosure of cash flow information:
Cash paid for interest	19,471	20,116	20,589
Cash paid for income taxes	$ 618	$ 556	$ 757

Organization and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization and Summary of Significant Accounting Policies

Note 1 — 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, with the exception of the income resulting from the upfront payment in April 2018 from our collaboration agreement with Bristol-Myers Squibb Company (BMS), we expect to continue to incur substantial losses and negative cash flows from operations in the future. We have financed our operations primarily through cash generated from licensing, collaboration and manufacturing agreements and financing transactions. At December 31, 2018, we had approximately $1.9 billion in cash and investments in marketable securities and had debt of $250.0 million in principal of senior secured notes due in October 2020.

Basis of Presentation, Principles of Consolidation and Use of Estimates

Our consolidated financial statements include the financial position, results of operations and cash flows of our wholly-owned subsidiaries: Nektar Therapeutics (India) Private Limited and Nektar Therapeutics UK Limited. All intercompany accounts and transactions have been eliminated in consolidation.

Our Consolidated Financial Statements are denominated in U.S. dollars. Accordingly, changes in exchange rates between the applicable foreign currency and the U.S. dollar will affect the translation of each foreign subsidiary’s financial results into U.S. dollars for purposes of reporting our consolidated financial results. Translation gains and losses are included in accumulated other comprehensive income (loss) in the stockholders’ equity section of the Consolidated Balance Sheets. To date, such cumulative translation adjustments have not been significant to our consolidated financial position. Aggregate gross foreign currency transaction gains (losses) recorded in operations for the years ended December 31, 2018, 2017, and 2016 were not significant.

The preparation of consolidated financial statements in conformity with U.S. generally accepted accounting principles (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Accounting estimates and assumptions are inherently uncertain. Actual results could differ materially from those estimates and assumptions. Our estimates include those related to estimated selling prices of performance obligations and estimates of variable consideration in collaboration agreements, estimated royalty revenue, other estimates required for revenue recognition as described further below, the net realizable value of inventory, the impairment of investments, goodwill and long-lived assets, contingencies, accrued clinical trial, contract manufacturing and other expenses, estimated non-cash royalty revenue and non-cash interest expense from our liability related to our sale of future royalties, stock-based compensation, and ongoing litigation, among other estimates. We base our estimates on historical experience and on other assumptions that management believes are reasonable under the circumstances. These estimates form the basis for making judgments about the carrying values of assets and liabilities when these values are not readily apparent from other sources. As appropriate, estimates are assessed each period and updated to reflect current information and any changes in estimates will generally be reflected in the period first identified.

Reclassifications

We have reclassified certain items previously reported in specific financial statement captions to conform to the current period presentation. Such reclassifications do not materially impact previously reported revenue, operating (income) loss, net (income) loss, total assets, liabilities or stockholders’ equity.

Cash, Cash Equivalents, and Investments, and Fair Value of Financial Instruments

We consider all investments in marketable securities with an original maturity of three months or less when purchased to be cash equivalents. We classify investments in securities with remaining maturities of less than one year, or where our intent is to use the investments to fund current operations or to make them available for current operations, as short-term investments. We classify investments in securities with remaining maturities of over one year as long-term investments.

Investments are designated as available-for-sale and are carried at fair value, with unrealized gains and losses reported in stockholders’ equity as accumulated other comprehensive income (loss). The disclosed fair value related to our cash equivalents and investments is based on market prices from a variety of industry standard data providers and generally represent quoted prices for similar assets in active markets or have been derived from observable market data.

We include interest on securities classified as available-for-sale, as well as amortization of premiums and accretion of discounts to maturity, in interest income. We include realized gains and losses and declines in value of available-for-sale securities judged to be other-than-temporary, if any, in other income (expense). The cost of securities sold is based on the specific identification method.

Our cash, cash equivalents, short-term investments and long-term investments are exposed to credit risk in the event of default by the third parties that hold or issue such assets. Our cash, cash equivalents, short-term investments and long-term investments are held by financial institutions that management believes are of high credit quality. Our investment policy limits investments to fixed income securities denominated and payable in U.S. dollars such as corporate bonds, corporate commercial paper, U.S. government obligations, and money market funds and places restrictions on maturities and concentrations by type and issuer.

Accounts Receivable and Significant Customer 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, and cost-sharing billings from collaborative research and development agreements. For the year ended December 31, 2018, our accounts receivable includes $24.2 million from contracts with customers and $19.0 million for net expense reimbursements from our collaboration partner. For the year ended December 31, 2017, our accounts receivable includes $3.3 million from contracts with customers and $1.7 million for expense reimbursements from our collaboration partner. We generally do not require collateral from our customers. We perform a regular review of our customers’ credit risk and payment histories, including payments made subsequent to year-end. When appropriate, we provide for an allowance for doubtful accounts by reserving for specifically identified doubtful accounts, although historically we have not experienced credit losses from our accounts receivable. At December 31, 2018, three customers represented 44%, 36% and 12%, respectively, of our accounts receivable. At December 31, 2017, four different customers represented 43%, 20%, 19% and 14%, respectively, of our accounts receivable.

Inventory and Significant Supplier Concentrations

Inventory is generally manufactured upon receipt of firm purchase orders from our collaboration partners. Inventory includes direct materials, direct labor, and manufacturing overhead and cost is determined on a first-in, first-out basis for raw materials and on a specific identification basis for work-in-process and finished goods. Inventory is valued at the lower of cost or net realizable value and defective or excess inventory is written down to net realizable value based on historical experience or projected usage. Inventory related to our research and development activities is expensed as manufactured by us or when purchased.

We are dependent on our suppliers and contract manufacturers to provide raw materials and drug candidates 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.

Long-Lived Assets

Property, plant and equipment are stated at cost, net of accumulated depreciation. Major improvements are capitalized, while maintenance and repairs are expensed when incurred. Manufacturing, laboratory and other equipment are depreciated using the straight-line method generally over estimated useful lives of three to ten years. Buildings are depreciated using the straight-line method generally over the estimated useful life of twenty years. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful life or the remaining term of the lease.

Goodwill represents the excess of the price paid for another entity over the fair value of the assets acquired and liabilities assumed in a business combination. We are organized in one reporting unit and evaluate the goodwill for the Company as a whole. Goodwill has an indefinite useful life and is not amortized, but instead tested for impairment at least annually in the fourth quarter of each year using an October 1 measurement date.

We assess the impairment of long-lived assets whenever events or changes in business circumstances indicate that the carrying amounts of the assets may not be fully recoverable. In the case of property, plant and equipment, we determine whether there has been an impairment by comparing the carrying value of the asset to the anticipated undiscounted net cash flows associated with the asset. If such cash flows are less than the carrying value, we write down the asset to its fair value, which may be measured as anticipated discounted net cash flows associated with the asset. In the case of goodwill impairment, we compare the carrying value of the reporting unit to its fair value, which we generally measure using market capitalization for our single reporting unit. If an impairment exists, we write down goodwill such that the carrying value of the reporting units equals its fair value.

Collaborative Arrangements

We enter into collaboration arrangements with pharmaceutical and biotechnology collaboration partners, under which we may grant licenses to our collaboration partners to further develop and commercialize one of our proprietary drug candidates, either alone or in combination with the collaboration partners’ compounds, or grant licenses to partners to use our technology to research and develop their own proprietary drug candidates. We may also perform research, development, manufacturing and supply activities under our collaboration agreements. Consideration under these contracts may include an upfront payment, development 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 Accounting Standards Codification (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. 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 collaboration partners. 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 an invoice. Our products are tested for adherence to technical specifications prior to 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.

Shipping and Handling Costs

We recognize costs related to shipping and handling of product to customers in cost of goods sold.

Research and Development Expense

Research and development costs are expensed as incurred and include salaries, benefits and other operating costs such as outside services, supplies and allocated overhead costs. We perform research and development for our proprietary drug candidates and technology development and for certain third parties under collaboration agreements. For our proprietary drug candidates and our internal technology development programs, we invest our own funds without reimbursement from a third party. Where we perform research and development activities under a clinical joint development collaboration, such as our collaboration with Bristol-Myers Squibb, we record the partner’s share of collaboration expenses 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 total estimated cost of the treatment phase on a per patient basis and we 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 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.

Advance payments for goods or services that will be used or rendered for future research and development activities are capitalized as prepaid expenses and recognized as expense as the related goods are delivered or the related services are 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. Such increases or decreases in cost are generally considered to be changes in estimates and will be reflected in research and development expenses in the period identified.

Stock-Based Compensation

Stock-based compensation arrangements include stock option grants and restricted stock unit (RSU) awards under our equity incentive plans, as well as shares issued under our Employee Stock Purchase Plan (ESPP), through which employees may purchase our common stock at a discount to the market price.

We use the Black-Scholes option pricing model for the respective grant to determine the estimated fair value of the option on the date of grant (grant date fair value) and the estimated fair value of common stock purchased under the ESPP. The Black-Scholes option pricing model requires the input of highly subjective assumptions. These variables include, but are not limited to, our stock price volatility over the term of the awards, and actual and projected employee stock option exercise behaviors. Because our employee stock options have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models may not provide a reliable single measure of the fair value of our employee stock options or common stock purchased under the ESPP. The fair value of an RSU is equal to the closing price of our common stock on the grant date. Management will continue to assess the assumptions and methodologies used to calculate the estimated fair value of stock-based compensation. Circumstances may change and additional data may become available over time, which could result in changes to these assumptions and methodologies, and which could materially impact our fair value determination.

We expense the value of the portion of the option or award on a straight line basis over the requisite service periods in our Consolidated Statements of Operations and recognize forfeitures of options and awards as they occur. For options and awards that vest upon the achievement of performance milestones, we estimate the vesting period based on our evaluation of the probability of achievement of each respective milestone and the related estimated date of achievement. Stock-based compensation expense for purchases under the ESPP is recognized over the respective six-month purchase period. Expense amounts are recorded in cost of goods sold, research and development expense, and general and administrative expense based on the function of the applicable employee. Stock-based compensation charges are non-cash charges and as such have no impact on our reported cash flows.

Net Income (Loss) Per Share

For all periods presented in the Consolidated Statements of Operations, the net income (loss) available to common stockholders is equal to the reported net income (loss). Basic net income (loss) per share is calculated based on the weighted-average number of common shares outstanding during the periods presented. Diluted net income (loss) per share is calculated based on the weighted-average number of shares of common stock outstanding, including potentially dilutive securities, which consist of common shares underlying stock options and restricted stock units (RSUs). For 2018, the effect of these dilutive securities under the treasury stock method was approximately 10.5 million, and we excluded approximately 3.3 million of weighted-average shares of common stock underlying outstanding stock options from the computation of diluted net income per share because their effect was antidilutive. For 2017 and 2016, basic and diluted net loss per share are the same due to our net losses and the requirement to exclude potentially dilutive securities which would have an antidilutive effect on net loss per share. We excluded weighted average outstanding stock options and RSUs totaling 20.6 million and 19.9 million during the years ended December 31, 2017 and 2016, respectively.

Income Taxes

We account for income taxes under the liability method. Under this method, we determine deferred tax assets and liabilities based on differences between the financial reporting and tax reporting bases of assets and liabilities, measured using enacted tax rates and laws that we expect to be in effect when we expect the differences to reverse. Realization of deferred tax assets is dependent upon future earnings, the timing and amount of which are uncertain. We record a valuation allowance against deferred tax assets to reduce their carrying value to an amount that is more likely than not to be realized. When we establish or reduce the valuation allowance related to the deferred tax assets, our provision for income taxes will increase or decrease, respectively, in the period we make such determination.

We utilize a two-step approach to recognize and measure uncertain tax positions. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates that it is more likely than not that the position will be sustained upon tax authority examination, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount of benefit, determined on a cumulative probability basis, that is more than 50% likely of being realized upon ultimate settlement.

Comprehensive income (loss)

Comprehensive income (loss) is the change in stockholders’ equity from transactions and other events and circumstances other than those resulting from investments by stockholders and distributions to stockholders. Our other comprehensive income (loss) includes net income (loss), gains and losses from the foreign currency translation of the assets and liabilities of our India and UK subsidiaries, and unrealized gains and losses on investments in available-for-sale securities.

Adoption of New Accounting Principle

On January 1, 2018, we adopted ASC 606, Revenue Recognition - Revenue from Contracts with Customers. ASC 606 supersedes the guidance in ASC 605, Revenue Recognition. Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine revenue recognition for units of account that an entity determines are within the scope of ASC 606, the entity performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. In our adoption, we used the practical expedients to analyze only those contracts that were still active contracts as of January 1, 2018 and evaluated those contracts based on the cumulative contract modifications through that date. We do not believe that the use of the practical expedients had or will have a material impact on our transition adjustment or our prospective accounting. We adopted ASC 606 on a modified retrospective basis under which we recognized the cumulative effect of adoption as a transition adjustment to opening accumulated deficit. Therefore, the periods prior to the adoption date of ASC 606 have not been restated.

The transition adjustment totaled $12.7 million, and included $10.7 million related to the recognition of royalty revenue. Previously, under ASC 605, we recognized certain of our royalty arrangements on a cash basis, generally one quarter in arrears. Beginning in the first quarter of 2018, we began to accrue our estimate of these royalties earned based on our collaboration partners’ sales of the associated drug compounds. As a result, in the first quarter of 2018, we recognized $11.1 million of estimated royalty revenue associated with our partners’ sales of MOVANTIK^® and ADYNOVATE^® in the first quarter of 2018. Previously, in the fourth quarter of 2017, we recognized $9.6 million in royalty revenue associated with sales of MOVANTIK^® and ADYNOVATE^® in the third quarter of 2017. The transition between the two accounting methods results in the $10.7 million in royalties for sales of MOVANTIK^® and ADYNOVATE^® in the fourth quarter of 2017 being recognized as a direct reduction of our accumulated deficit instead of being recognized in the statement of operations. The transition adjustment also includes $2.0 million for the reduction of deferred revenue related to one of our collaboration arrangements. The impact of the adoption of ASC 606 on our Consolidated Balance Sheet as of December 31, 2018 and Consolidated Statement of Operations data for the year ended December 31, 2018 was as follows (in thousands):


	As reported			Adjustments			Balances Without the Adoption of Topic 606
Consolidated Balance Sheet data as of December 31, 2018
Accounts receivable, net	$	43,213		$	(21,030	)	$	22,183
Deferred revenue, current portion		13,892			1,191			15,083
Deferred revenue, less current portion		10,744			(112	)		10,632
Accumulated deficit		(1,424,051	)		(22,109	)		(1,446,160	)

Consolidated Statement of Operations data for the year ended December 31, 2018
Product sales	$	20,774		$	(192	)	$	20,582
Royalty revenue		41,976			(286	)		41,690
License, collaboration and other revenue		1,097,265			(8,934	)		1,088,331
Total revenue		1,193,323			(9,412	)		1,183,911

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 February 2016, the FASB issued guidance to amend a number of aspects of lease accounting, including requiring lessees to recognize almost all leases with a term greater than one year as a right-of-use asset and corresponding liability, measured at the present value of the lease payments. The guidance will become effective for us beginning in the first quarter of 2019 and is required to be adopted using a modified retrospective approach. The adoption of this guidance will have a material effect on our balance sheet. In particular, for our facilities leases described in Note 6, we expect to recognize right-of-use assets, estimated between $87 million and $97 million and lease liabilities, estimated between $96 million and $106 million. The estimate for the right-of-use assets reflects the estimated lease liabilities, reduced by our historical deferred rent balance, which, as discussed in Note 6, totaled $9.3 million as of December 31, 2018.

Cash and Investments in Marketable Securities

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Cash and Investments in Marketable Securities

Note 2 — Cash and Investments in Marketable Securities

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

	Estimated Fair Value at
	December 31, 2018		December 31, 2017
Cash and cash equivalents	$	194,905	$	4,762
Short-term investments		1,140,445		291,370
Long-term investments		582,889		57,088
Total cash and investments in marketable securities	$	1,918,239	$	353,220

We invest in liquid, high quality debt securities. Our investments in debt securities are subject to interest rate risk. To minimize the exposure due to an adverse shift in interest rates, we invest in securities with maturities of two years or less and maintain a weighted average maturity of one year or less. All of our long-term investments as of December 31, 2018 and 2017 had maturities between one and two years.

Gross unrealized gains and losses were not significant at either December 31, 2018 or 2017. During the years ended December 31, 2018, 2017 and 2016, we sold available-for-sale securities totaling $12.0 million, $37.5 million, and $5.0 million, respectively, and realized gains and losses were not significant in any of those periods.

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		December 31, 2018		December 31, 2017
Corporate notes and bonds		2	$	1,288,986	$	216,253
Corporate commercial paper		2		498,048		128,096
Obligations of U.S. government agencies		2		12,977		2,977
Available-for-sale investments				1,800,011		347,326
Money market funds		1		105,656		302
Certificate of deposit	N/A			6,760		1,132
Cash	N/A			5,812		4,460
Total cash and investments in marketable securities			$	1,918,239	$	353,220

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.

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.

During the years ended December 31, 2018 and 2017, there were no transfers between Level 1 and Level 2 of the fair value hierarchy.

At December 31, 2018 and 2017, we had letter of credit arrangements in favor of our landlords and certain vendors totaling $6.6 million and $1.1 million, respectively. These letters of credit are secured by investments of similar amounts.

- Definition

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

+ References + Details

Inventory

12 Months Ended

Dec. 31, 2018

Inventory Disclosure [Abstract]

Inventory

Note 3 — Inventory

Inventory consists of the following (in thousands):

	December 31,
	2018		2017
Raw materials	$	1,846	$	1,796
Work-in-process		6,403		4,843
Finished goods		3,132		4,087
Total inventory	$	11,381	$	10,726

Property, Plant and Equipment

12 Months Ended

Dec. 31, 2018

Property Plant And Equipment [Abstract]

Property, Plant and Equipment

Note 4 — Property, Plant and Equipment

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

	December 31,
	2018			2017
Building and leasehold improvements	$	77,771		$	81,444
Laboratory equipment		33,806			31,214
Computers, furniture, and other		31,354			27,800
Manufacturing equipment		21,339			20,695
Depreciable property, plant and equipment at cost		164,270			161,153
Less: accumulated depreciation		(120,507	)		(115,090	)
Depreciable property, plant and equipment, net		43,763			46,063
Construction-in-progress		5,088			1,400
Property, plant and equipment, net	$	48,851		$	47,463

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

Depreciation and amortization expenses on property, plant and equipment for the years ended December 31, 2018, 2017, and 2016 was $8.8 million, $12.6 million, and $13.2 million, respectively.

In November 2017, Bayer announced that the Phase 3 Amikacin Inhale clinical program did not meet its primary endpoint or key secondary endpoints and, in December 2017, Bayer terminated our related collaboration agreement. Under this collaboration, we were responsible for the development, manufacturing and supply of our proprietary nebulizer device included in the Amikacin product and had acquired specific manufacturing equipment for this purpose. As a result of the termination of the program, in the three months ended December 31, 2017, we expensed program specific manufacturing equipment with an original cost of $23.4 million and a net book value of $15.1 million. We completed the disposal of this equipment in the first quarter of 2018. In addition, in the three months ended December 31, 2017, we incurred approximately $0.9 million of other program termination costs related to our manufacturing obligations.

Senior Secured Notes

12 Months Ended

Dec. 31, 2018

Debt Disclosure [Abstract]

Senior Secured Notes

Note 5 — Senior Secured Notes

On October 5, 2015, we completed the sale and issuance of $250.0 million in aggregate principal amount of 7.75% senior secured notes due 2020 (the Notes). The Notes are secured by a first-priority lien on substantially all of our assets and bear interest at a rate of 7.75% per annum payable in cash quarterly in arrears on January 15, April 15, July 15, and October 15 of each year. Interest is calculated based on actual days outstanding over a 360 day year. The Notes will mature on October 5, 2020, at which time the outstanding principal will be due and payable.

In connection with the issuance of the Notes, we paid fees and expenses of $8.9 million, of which $8.7 million of transaction and facility fees paid directly to the purchasers of the Notes and other direct issuance costs were capitalized as a debt discount and issuance costs and are recorded as a reduction to the senior secured notes, net liability balance in our Consolidated Balance Sheet. The unamortized balance of these costs is $3.1 million at December 31, 2018 and will be amortized to interest expense over the remaining term of the Notes.

The agreement, pursuant to which the Notes were issued, contains customary covenants, including covenants that limit or restrict our ability to incur liens, incur indebtedness, declare or pay dividends, redeem stock, issue preferred stock, make certain investments, merge or consolidate, make dispositions of assets, or enter into certain new businesses or transactions with affiliates, but do not contain covenants related to future financial performance. In particular, the Notes agreement requires us to maintain a minimum cash and investments in marketable securities balance of $60.0 million during the term of the Notes. We may currently redeem some or all of these notes at a redemption price equal to 102% of the principal amount of the notes if the redemption date is prior to October 5, 2019, or 100% of the principal amount of the notes if the redemption date is on or after October 5, 2019, plus, in each case, accrued and unpaid interest to the applicable redemption date. If we experience certain change of control events, the holders of the Notes will have the right to require us to purchase all or a portion of the Notes at a purchase price in cash equal to 101% of the principal amount thereof, plus accrued and unpaid interest to the date of purchase. In addition, upon certain asset sales, we may be required to offer to use the net proceeds thereof to purchase some of the Notes at 100% of the principal amount thereof, plus accrued and unpaid interest to the date of purchase.

As of December 31, 2018, based on a discounted cash flow analysis using Level 3 inputs including financial discount rates, we estimate that the fair value of the Notes is approximately $258.0 million.

Leases

12 Months Ended

Dec. 31, 2018

Leases [Abstract]

Leases

Note 6 — Leases

Operating 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 134,356 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 January 31, 2030, subject to our right to extend the term of the lease for two consecutive five-year periods. 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 insurance costs and taxes. The Mission Bay Lease also obligates us to rent from ARE a total of an additional approximately 18,000 square feet of space at the Mission Bay Facility at specified delivery dates. 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. 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. An initial 1,726 square feet was delivered in June 2018, and a total of 67,105 square feet for two additional spaces was delivered in December 2018. The remaining space will be delivered in phases during 2019. The Third Street Lease will provide us additional facilities to support increased personnel for our San Francisco-based R&D activities. The lease term includes a right to extend the term for a consecutive five-year period. Our fixed annual 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 onetime 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.

We recognize rent expense on a straight-line basis over the lease period. For the years ended December 31, 2018, 2017 and 2016, rent expense totaled approximately $8.1 million, $4.7 million and $3.2 million, respectively. As of December 31, 2018 and 2017, we had total deferred rent balances of $9.3 million and $6.0 million, respectively, which we present in other long-term liabilities in our Consolidated Balance Sheets.

Our future minimum lease payments for our operating leases at December 31, 2018 are as follows (in thousands):

Year ending December 31,
2019	$	7,914
2020		10,617
2021		13,649
2022		14,117
2023		14,599
2024 and thereafter		98,315
Total future minimum lease payments	$	159,211

Liability Related to the Sale of Future Royalties

12 Months Ended

Dec. 31, 2018

Note 7 — Liability Related to the 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 will be 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 will continue to account for these royalties as revenue, and we recorded the $124.0 million in proceeds from this transaction as a liability (Royalty Obligation) that will be amortized using the interest method over the estimated life of the Purchase and Sale Agreement.

The following table shows the activity within the liability account during the year ended December 31, 2018 and for the period from the inception of the royalty transaction on February 24, 2012 (inception) to December 31, 2018 (in thousands):

	Year ended December 31, 2018			Period from inception to December 31, 2018
Liability related to the sale of future royalties—beginning balance	$	96,922		$	—
Proceeds from sale of future royalties		—			124,000
Payments from Nektar to RPI		—			(10,000	)
Non-cash CIMZIA^® and MIRCERA^® royalty revenue		(33,308	)		(170,839	)
Non-cash interest expense recognized		21,196			141,649
Liability related to the sale of future royalties – ending balance		84,810			84,810
Less: unamortized transaction costs		(1,899	)		(1,899	)
Liability related to the sale of future royalties, net	$	82,911		$	82,911

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

During the years ended December 31, 2018, 2017 and 2016, we recognized $33.3 million, $30.5 million, and $30.2 million, respectively, in non-cash royalties from net sales of CIMZIA^® and MIRCERA^®, and we recorded $21.2 million, $18.9 million and $19.7 million, respectively, of related non-cash interest expense.

As royalties are remitted to RPI from Roche and UCB, the balance of the Royalty Obligation will be effectively repaid over the life of the agreement. In order to determine the amortization of the Royalty Obligation, we are required to estimate the total amount of future royalty payments to be received by RPI. The sum of these amounts less the $124.0 million proceeds we received will be recorded as interest expense over the life of the Royalty Obligation. From inception until 2017, our estimate of this total interest expense resulted in an effective annual interest rate of approximately 17%. We periodically assess the estimated royalty payments to RPI from UCB and Roche and to the extent the amount or timing of such payments is materially different than our original estimates, we will prospectively adjust the amortization of the Royalty Obligation. During the three month period ended December 31, 2017, as a result of increases in the forecasted sales of CIMZIA^®, 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 21%. During the three month period 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%.

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

In addition, 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

12 Months Ended

Dec. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

Note 8 — Commitments and Contingencies

Purchase Commitments

In the normal course of business, we enter into various firm purchase commitments related to contract manufacturing, clinical development and certain other items. As of December 31, 2018, these commitments were approximately $63.3 million, all of which we expect to pay in 2019.

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 our CEO and CFO were named in a putative securities class action entitled, Mulquin v. Nektar Therapeutics et. al., N.D. Cal. 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. These cases are in the early stages. Accordingly, we cannot reasonably estimate any range of potential future charges. However, an unfavorable resolution could potentially have a material adverse effect on our business, financial condition, and results of operations or prospects, potentially delay or limit our ability to use some of our research and development programs, and potentially result in paying monetary damages. We have recorded no liability for these matters on our Consolidated Balance Sheets as of December 31, 2018.

Foreign Operations

We operate in a number of foreign countries. As a result, we are subject to numerous local laws and regulations that can result in claims made by foreign government agencies or other third parties that are often difficult to predict even after the application of good faith compliance efforts.

Indemnification Obligations

During the course of our normal operating activities, we have agreed to certain contingent indemnification obligations as further described below. The term of our indemnification obligations is generally perpetual. There is generally no limitation on the potential amount of future payments we could be required to make under these indemnification obligations. To date, we have not incurred significant costs to defend lawsuits or settle claims based on our indemnification obligations. If any of our indemnification obligations is triggered, we may incur substantial liabilities. Because the aggregate amount of any potential indemnification obligation is not a stated amount, we cannot reasonably estimate the overall maximum amount of any such obligations. We have recorded no liabilities for these obligations on our Consolidated Balance Sheets as of December 31, 2018 or 2017.

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 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. For example, as part of the sale of our royalty interest in the CIMZIA^® and MIRCERA^® products, we and RPI made representations and warranties and entered into certain covenants and ancillary agreements which are supported by indemnity obligations. If it is determined that we breached certain of the representations and warranties or covenants and agreements made by us in any such agreements, we could incur substantial indemnification liabilities depending on the timing, nature, and amount of any such claims.

Indemnification of Underwriters and Initial Purchasers of our Securities

In connection with our sale of equity and senior secured debt securities, we have agreed to defend, indemnify and hold harmless our underwriters or initial purchasers, as applicable, as well as certain related parties from and against certain liabilities, including liabilities under the Securities Act of 1933, as amended.

Director and Officer Indemnifications

As permitted under Delaware law, and as set forth in our Certificate of Incorporation and our Bylaws, we indemnify our directors, executive officers, other officers, employees, and other agents for certain events or occurrences that may arise while in such capacity. The maximum potential amount of future payments we could be required to make under this indemnification is unlimited; however, we have insurance policies that may limit our exposure and may enable us to recover a portion of any future amounts paid. Assuming the applicability of coverage, the willingness of the insurer to assume coverage, and subject to certain retention, loss limits and other policy provisions, we believe any obligations under this indemnification would not be material, other than up to $2.5 million per incident for merger and acquisition related claims, $2.5 million per incident for securities related claims and $1.25 million per incident for non-securities related claims retention deductible per our insurance policy. However, no assurances can be given that the covering insurers will not attempt to dispute the validity, applicability, or amount of coverage without expensive litigation against these insurers, in which case we may incur substantial liabilities as a result of these indemnification obligations.

Stockholders' Equity

12 Months Ended

Dec. 31, 2018

Equity [Abstract]

Stockholders' Equity

Note 9 — Stockholders’ Equity

Common Stock

As discussed in Note 10, on April 3, 2018, we completed the issuance and sale of 8,284,600 shares of our common stock under a Share Purchase Agreement with BMS. These shares are unregistered and subject to certain lock-up and stand-still provisions for a five-year period.

On October 24, 2016, we completed the issuance and sale of 14,950,000 shares of our common stock in an underwritten public offering with total proceeds of approximately $189.7 million after deducting the underwriting commissions and discounts of approximately $12.1 million. In addition, we incurred approximately $0.4 million in legal and accounting fees, filing fees, and other costs in connection with this offering.

Equity Compensation Plans

At December 31, 2018, we had 31,940,416 reserved shares of common stock, all of which are reserved for issuance under our equity compensation plans, of which approximately 19,250,000 shares may be issued upon the exercise of outstanding options or the vesting of restricted stock units (RSUs) and 12,690,000 shares are available for issuance under equity compensation plans.

2017 Performance Incentive Plan

Our 2017 Performance Incentive Plan (2017 Plan) was adopted by our board of directors (Board of Directors) on March 28, 2017 and was approved by our stockholders on June 14, 2017. On the date of approval, any shares of our common stock that were available for issuance under our 2012 Performance Incentive Plan (2012 Plan) ceased to be available for future grants.

Subject to the terms of the 2017 Plan, 8,300,000 shares of our common stock, reduced by the number of shares of common stock subject to awards granted under the 2012 Plan on or after March 31, 2017 and prior to the adoption of the 2017 Plan, were initially available for awards under the 2017 Plan. On June 26, 2018, our stockholders approved an amendment to the 2017 Plan whereby 10,900,000 additional shares were made available for award grants under the 2017 Plan. Shares issued in respect of any “full-value award” granted under the 2017 Plan will be counted against the share limit described in the preceding sentences as 1.5 shares for every one share actually issued in connection with the award. Shares that are subject to or underlie awards which expire or for any reason are cancelled or terminated, are forfeited, fail to vest, or for any other reason are not paid or delivered under the 2017 Plan or any Prior Plan (as defined below) will again be available for subsequent awards under the 2017 Plan (with any such shares subject to full-value awards increasing the 2017 Plan’s share limit based on the full-value award ratio described above or, in the case of an award granted under a Prior Plan, the full-value award ratio set forth in such Prior Plan). Notwithstanding the foregoing, shares that are exchanged by a participant or withheld by us to pay the exercise price of an award granted under the 2017 Plan, as well as any shares exchanged or withheld to satisfy the tax withholding obligations related to any award, will not be available for subsequent awards under the 2017 Plan.

The purpose of the 2017 Plan and our other incentive plans is to promote our success by providing an additional means for us to attract, motivate, retain and reward directors, officers, employees, and other eligible persons through the grant of awards. Equity-based awards are also intended to further align the interests of award recipients and our stockholders. The 2017 Plan authorizes stock options, stock appreciation rights, stock bonuses, restricted stock, performance stock, stock units, phantom stock or similar rights to purchase or acquire shares, and other forms of awards granted or denominated in our common stock or units of our common stock, as well as cash bonus awards. Members of the Board of Directors, officers or employees, certain consultants and advisors and our subsidiaries are eligible to receive awards under the 2017 Plan. Pursuant to the 2017 Plan, we granted or issued non-qualified stock options and RSUs to employees, officers, and non-employee directors during 2017 and 2018. The requisite service period for stock options granted to our employees under the 2017 Plan as well as our Prior Plans is generally four years; the requisite service period for stock options granted to our directors is generally one year. The requisite service period for RSUs granted under the 2017 Plan and our Prior Plans is generally three years for employees and one year for directors.

The 2017 Plan will terminate on March 27, 2027, unless earlier terminated by the Board of Directors. The maximum term of a stock option or stock appreciation right under the 2017 Plan and our Prior Plans is eight years from the date of grant. The per share exercise price of an option generally may not be less than the fair market value of a share of our common stock on The NASDAQ Stock Market on the date of grant.

Other Equity Incentive Plans

In addition to the 2017 Plan, we have other equity incentive plans under which options and restricted stock units granted remain outstanding but no new options or restricted stock units may be granted either as a result of the effectiveness of the 2017 Plan or the expiration of such other plan. These other equity incentive plans include: (i) the 2012 Plan which was adopted by the Board of Directors on April 4, 2012 and approved by our stockholders on June 28, 2012, and replaced by the 2017 Plan; (ii) the 2008 Equity Incentive Plan (2008 Plan) which was adopted by the Board of Directors on March 20, 2008 and approved by our stockholders on June 6, 2008; and (iii) the 1998 Non-Officer Equity Incentive Plan which was adopted by our Board of Directors on August 18, 1998, and amended and restated in its entirety and renamed the 2000 Non-Officer Equity Incentive Plan on June 6, 2000 (2000 Non-Officer Plan and collectively with the 2012 Plan and the 2008 Plan, the Prior Plans).

Pursuant to the Prior Plans, we previously granted or issued incentive stock options to employees and officers and non-qualified stock options, rights to acquire restricted stock, restricted stock units, and stock bonuses to employees, officers, non-employee directors, and consultants.

Employee Stock Purchase Plan

In February 1994, our Board of Directors adopted the Employee Stock Purchase Plan (ESPP) pursuant to section 423(b) of the Internal Revenue Code of 1986. Under the ESPP, 2,500,000 shares of our common stock have been authorized for issuance. The terms of the ESPP provide eligible employees with the opportunity to acquire an ownership interest in Nektar through participation in a program of periodic payroll deductions for the purchase of our common stock. Employees may elect to enroll or re-enroll in the ESPP on a semi-annual basis. Stock is purchased at 85% of the lower of the closing price on the first day of the enrollment period or the last day of the enrollment period.

401(k) Retirement Plan

We sponsor a 401(k) retirement plan whereby eligible employees may elect to contribute up to the lesser of 60% of their annual compensation or the statutorily prescribed annual limit allowable under Internal Revenue Service regulations. The 401(k) plan permits us to make matching contributions on behalf of all participants, up to a maximum of $6,000 per participant. For the years ended December 31, 2018, 2017, and 2016, we recognized $2.8 million, $1.6 million, and $1.1 million, respectively, of compensation expense in connection with our 401(k) retirement plan.

Change in Control Severance Plan

On December 6, 2006, our Board of Directors approved a Change of Control Severance Benefit Plan (CIC Plan). This CIC Plan has subsequently been amended a number of times by our Board of Directors with the most recent amendment occurring on April 5, 2011. The CIC Plan is designed to make certain benefits available to our eligible employees in the event of a change of control of Nektar and, following such change of control, an employee’s employment with us or a successor company is terminated in certain specified circumstances. We adopted the CIC Plan to support the continuity of the business in the context of a change of control transaction. The CIC Plan was not adopted in contemplation of any specific change of control transaction.

Under the CIC Plan, in the event of a change of control of Nektar and a subsequent termination of employment initiated by us or a successor company other than for Cause (as defined in the CIC Plan) or initiated by the employee for a Good Reason Resignation (as defined in the CIC Plan) in each case within twelve months following a change of control transaction, (i) the Chief Executive Officer would be entitled to receive cash severance pay equal to 24 months base salary plus annual target incentive pay, the extension of employee benefits over this severance period and the full acceleration of unvested outstanding equity awards, and (ii) our Senior Vice Presidents and Vice Presidents (including Principal Fellows) would each be entitled to receive cash severance pay equal to twelve months base salary plus annual target incentive pay, the extension of employee benefits over this severance period and the full acceleration of unvested outstanding equity awards. In the event of a change of control of Nektar and a subsequent termination of employment initiated by the Company or a successor company other than for Cause within twelve months following a change of control transaction, all other employees would each be entitled to receive cash severance pay equal to six months base salary plus a pro-rata portion of annual target incentive pay, the extension of employee benefits over this severance period and the full acceleration of each such employee’s unvested outstanding equity awards. Under the CIC Plan, as amended, non-employee directors would also be entitled to full acceleration of vesting of all outstanding stock awards in the event of a change of control transaction.

License and Collaboration Agreements

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

License and Collaboration Agreements

Note 10 — 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. All of our collaboration agreements are generally cancelable by our partners without significant financial penalty. Our costs of performing these services are generally included in research and development expense, except that costs for product sales to our collaboration partners are included in cost of goods sold. We analyze our agreements to determine whether we should account for the agreements within the scope of ASC 808, Collaborative Arrangements, and, if so, we analyze whether we should account for any elements under the relevant revenue recognition guidance or whether we should record the reimbursements from our partner as contra research and development expense. As described in Note 1, on January 1, 2018, we adopted ASC 606, Revenue Recognition - Revenue from Contracts with Customers, which supersedes the guidance in ASC 605, Revenue Recognition. We recognized revenue under ASC 606 for the year ended December 31, 2018 and under ASC 605 for the years ended December 31, 2017 and 2016. In the year ended December 31, 2018, we recognized $95.3 million of revenue for performance obligations that we had satisfied in prior periods. This amount includes all of our royalty revenue, non-cash royalty revenue and the $10.0 million ADYNOVATE^® sales milestone because these revenues substantially relate to the licenses that we had previously granted. This amount also includes the $10.0 million development milestone payment earned from Baxalta described below.

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

		Year Ended December 31,
Partner	Agreement	2018		2017		2016
Bristol-Myers Squibb	NKTR-214	$	1,059,768	$	—		—
Baxalta Incorporated / Takeda	Hemophilia, including ADYNOVATE^® and ADYNOVI^TM		20,328		11,443		650
Eli Lilly and Company	NKTR-358		11,634		130,087		—
Amgen, Inc.	Neulasta^®		5,000		5,000		5,000
Ophthotech Corporation⁽¹⁾	Fovista^®		—		19,123		1,408
Bayer Healthcare LLC⁽¹⁾	BAY41-6551 (Amikacin Inhale)		—		17,931		1,429
AstraZeneca AB	MOVANTIK^®and MOVENTIG^®		—		4,600		33,000
Other			535		22,781		18,895
License, collaboration and other revenue		$	1,097,265	$	210,965	$	60,382

(1)	These collaboration agreements were completed as of December 31, 2017.

The following table presents the changes in our deferred revenue balance from our collaboration agreements during the year ended December 31, 2018 (in thousands):

	For the year ended December 31, 2018
Deferred revenue—December 31, 2017	$	37,970
Transition adjustment related to adoption of ASC 606		(1,953	)
Additions to deferred revenue		5,950
Recognition of previously unearned revenue		(17,331	)
Deferred revenue—December 31, 2018	$	24,636

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 $13.9 million of our deferred revenue over the next twelve months and recognize approximately half of the remaining $10.7 million over the following twelve months.

As of December 31, 2018, our collaboration agreements with partners included potential future payments for development milestones totaling approximately $1.7 billion, including amounts from our agreements with BMS and Lilly described below. In addition, under our collaboration agreements we are entitled to receive other contingent payments, including contingent sales milestones and royalty payments, as described below.

Bristol-Myers Squibb (BMS): NKTR-214

On February 13, 2018, we entered into a Strategic Collaboration Agreement with BMS (BMS Collaboration Agreement) and Share Purchase Agreement, both of which became effective on April 3, 2018. Pursuant to these agreements, we and BMS will jointly develop 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 production 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 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 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 expenses as a reduction of research and development expense and our reimbursement of BMS’ expenses as research and development expense. For the year ended December 31, 2018 and 2017, we recorded $62.5 million and $7.8 million, respectively, as a reduction of research and development expenses for BMS’ share of our expenses, net of our share of BMS’ expenses. As of December 31, 2018, we have recorded a receivable of $19.0 million from BMS in accounts receivable in our 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 per share, 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 as of December 31, 2018 because we determined such payments to be fully constrained under ASC 606 as the achievement of such milestone payments are uncertain and highly susceptible to factors outside of our control. We will 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 for the year ended December 31, 2018 as license, collaboration and other revenue.

Baxalta Incorporated/Takeda: Hemophilia

We are a party to an exclusive research, development, license and manufacturing and supply agreement with Baxalta Incorporated (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 of 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 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 was received in March 2018. In the three months ended December 31, 2018, we recognized an additional $10.0 million milestone for annual sales of ADYNOVATE^®/ADYNOVI^TM reaching a certain specified amount. We are entitled to an additional sales milestone upon achievement of an annual sales target and royalties based on annual 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.

Under our adoption of ASC 606 as of January 1, 2018, we determined that our satisfied performance obligations consist of granting the license, granting the right to sublicense and performing research and development services. We determined that we have an unsatisfied performance obligation related to our ongoing supply of PEGylation materials at a price less than their standalone selling prices. We updated the arrangement transaction price for the $10.0 million EU approval milestone upon achievement 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 year ended December 31, 2018 as we had previously satisfied those performance obligations. As of December 31, 2018, we have accounts receivable of $15.4 million and deferred revenue of $0.8 million related to this agreement.

Eli Lilly and Company (Lilly): NKTR-358

Effective August 23, 2017, we entered into a worldwide license agreement with Eli Lilly and Company (Lilly) 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 with Nektar 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 Nektar, (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 to us 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, our drug product development obligation and our obligation to supply clinical trial materials as the significant performance obligations under the agreement and concluded that each of these deliverables represents a separate unit of accounting. 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 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, we did not include any of such milestones in 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.

Under our adoption of ASC 606 as of January 1, 2018, we made no changes to our deferred revenue balance. We concluded that it was appropriate to have 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 December 31, 2018, we have deferred revenue of approximately $8.3 million related to this agreement, which we expect to recognize through December 2019, the estimated end of our performance obligations under this agreement.

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 guarantee the manufacture and supply of our proprietary PEGylation materials (Polymer Materials) to Amgen in an existing manufacturing suite to be used exclusively for the manufacture of Polymer Materials for Amgen (the Manufacturing Suite) in our manufacturing facility in Huntsville, Alabama (the Facility). This supply arrangement is on a non-exclusive basis (other than the use of the Manufacturing Suite and certain equipment) whereby we are free to manufacture and supply the Polymer Materials to any other third party and Amgen is free to procure the Polymer Materials from any other third party. 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 Polymer Materials to Amgen including without limitation the Additional Rights described below and manufacturing fees that are calculated based on fixed and variable components applicable to the Polymer Materials ordered by Amgen and delivered by us. Amgen has no minimum purchase commitments. If quantities of the Polymer Materials ordered by Amgen exceed specified quantities, significant additional payments become payable to us in return for our guaranteeing the supply of additional quantities of the Polymer Materials.

The term of the amended and restated agreement ends on October 29, 2020. In the event we become subject to a bankruptcy or insolvency proceeding, we cease to own or control the Facility, we fail to manufacture and supply or certain other events, Amgen or its designated third party will have the right to elect, among certain other options, to take title to the dedicated equipment and access the Facility to operate the Manufacturing Suite solely for the purpose of manufacturing the Polymer Materials. Amgen may terminate the amended and restated agreement for convenience or due to an uncured material default by us.

Under our adoption ASC 606 as of January 1, 2018, we determined that our obligation to manufacture and supply of 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 December 31, 2018, we have deferred revenue of approximately $9.2 million related to this agreement, which we expect to recognize through October 2020, the estimated end of our obligations under this agreement.

Ophthotech Corporation: Fovista^®

On October 27, 2017, we terminated our license and supply agreement with Ophthotech Corporation (Ophthotech) dated September 2006, pursuant to which Ophthotech received a worldwide, exclusive license to certain of our proprietary PEGylation technology to develop, manufacture and sell Fovista^®. Under the terms of our agreement, we were the exclusive supplier of all of Ophthotech’s clinical and commercial requirements for our proprietary PEGylation reagent used in Fovista^®. The termination of our agreement with Ophthotech followed Opthotech’s previous announcements, in December 2016 and August 2017, that their three pivotal Phase 3 studies investigating the superiority of Fovista^® therapy in combination with Lucentis^® therapy compared to Lucentis^® monotherapy and evaluating Fovista^® in combination with Eylea^® or Avastin^® compared to Eylea^® or Avastin^® monotherapy for the treatment of wet age-related macular degeneration (AMD) did not achieve the pre-specified primary endpoints.

Under our agreement with Ophthotech, in June 2014, we received a $19.8 million payment from Ophthotech in connection with its licensing agreement with Novartis. In addition, in January 2017, we received a $12.7 million advance payment from Ophthotech, which included $10.4 million for reagent shipments recognized in the second quarter of 2017 as well as approximately $2.3 million for 2017 minimum purchase requirements. As a result of the termination of this agreement, we recognized the remaining $18.0 million of deferred revenue from this arrangement in the three months ended December 31, 2017.

Bayer Healthcare LLC: BAY41-6551 (Amikacin Inhale)

In December 2017, Bayer Healthcare LLC (Bayer) terminated our co-development, license and co-promotion agreement entered into in August 2007 to develop a specially-formulated inhaled Amikacin. Under this agreement, we were responsible for development, manufacturing and supply of our proprietary nebulizer device included in the Amikacin product. Bayer was responsible for most clinical development and commercialization activities and costs, all activities and costs to support worldwide regulatory filings, approvals and related activities, further development of Amikacin Inhale and final product packaging and distribution. The termination of this agreement followed Bayer’s announcement in November 2017 that the Phase 3 Amikacin Inhale clinical program for the treatment of intubated and mechanically ventilated patients with Gram-negative pneumonia did not meet its primary endpoint or key secondary endpoints.

Under this collaboration, we received an upfront payment of $40.0 million (which was paid to us in 2007) and milestone payments totaling $30.0 million (the last of which was paid to us in 2013). As a result of the termination of the agreement, we recognized the remaining $16.8 million of deferred revenue related to this arrangement in the three months ended December 31, 2017.

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 and is responsible for all drug development and commercialization decisions for MOVANTIK^®. In September 2014 and December 2014, MOVANTIK^® /MOVENTIG^® was approved in the US and EU, respectively. As of December 31, 2018, 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. We are entitled to significant and escalating double-digit royalty payments and sales milestone payments based on annual worldwide net sales of MOVANTIK^® / MOVENTIG^®.

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%. In the years ended December 31, 2017 and 2016, we recognized a total of $4.6 million and $33.0 million, respectively, related to our share of license-related payments made from Kirin to AstraZeneca. As of December 31, 2018, we do not have deferred revenue related to our agreement with AstraZeneca.

Other

In addition, as of December 31, 2018, we have a number of other collaboration agreements, including with our collaboration partners UCB and Halozyme Therapeutics, Inc., under which we are entitled to up to a total of $45.5 million of development milestones 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. As of December 31, 2018, we have deferred revenue of approximately $6.4 million related to these other collaboration agreements.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2018

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note 11 — Stock-Based Compensation

We issue stock-based awards from our equity incentive plans, which are more fully described in Note 9. Stock-based compensation expense was recognized as follows (in thousands):

	Year Ended December 31,
	2018		2017		2016
Cost of goods sold	$	4,629	$	2,333	$	1,620
Research and development		56,193		21,252		13,093
General and administrative		27,279		13,030		11,137
Total stock-based compensation	$	88,101	$	36,615	$	25,850

As of December 31, 2018, total unrecognized compensation costs of $258.4 million related to unvested stock-based compensation arrangements are expected to be recognized as expense over a weighted-average period of 1.9 years.

Stock-based compensation expense resulting from our ESPP was not significant in the years ended December 31, 2018, 2017, and 2016.

Black-Scholes Assumptions

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

	Year Ended December 31,
	2018			2017			2016
Average risk-free interest rate		2.8	%		2.0	%		1.4	%
Dividend yield		0.0	%		0.0	%		0.0	%
Average volatility factor		61.0	%		54.2	%		51.7	%
Average weighted average expected life	5.1 years			5.3 years			5.3 years

The average risk-free interest rate is based on the U.S. treasury yield curve in effect at the time of grant for periods commensurate with the expected life of the stock-based award. We have never paid dividends, nor do we expect to pay dividends in the foreseeable future; therefore, we used a dividend yield of zero. Our estimate of expected volatility is based on the daily historical trading data of our common stock at the time of grant over a historical period commensurate with the expected life of the stock-based award. We estimated the weighted-average expected life based on the contractual and vesting terms of the stock options, as well as historical cancellation and exercise data.

Summary of Stock Option Activity

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

	Number of Shares			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Life (in Years)		Aggregate Intrinsic Value(1)
Outstanding at December 31, 2017		18,826		$	20.35
Options granted		1,846			55.35
Options exercised		(4,374	)		13.24
Options forfeited & canceled		(368	)		27.75
Outstanding at December 31, 2018		15,930		$	26.18		4.96	$	214,525

Exercisable at December 31, 2018		9,393			16.16		3.69	$	173,436

(1)	Aggregate intrinsic value represents the difference between the exercise price of the option and the closing market price of our common stock on December 31, 2018.

The weighted-average grant-date fair value per share of options granted during the years ended December 31, 2018, 2017, and 2016 was $29.86, $20.08, and $6.54, respectively. The total intrinsic value of options exercised during the years ended December 31, 2018, 2017, and 2016 was $303.4 million, $84.0 million, and $17.9 million, respectively. The estimated fair value of options vested during the years ended December 31, 2018, 2017, and 2016 was $39.0 million, $19.3 million, and $16.7 million, respectively.

Summary of RSU Activity

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

	Units Issued			Weighted- Average Grant Date Fair Value		Aggregate Intrinsic Value(1)
Balance at December 31, 2017		2,578		$	35.52
Granted		2,125			41.67
Vested and released		(1,255	)		29.44
Forfeited and canceled		(128	)		40.39
Balance at December 31, 2018		3,320		$	41.57	$	109,125

(1)	Aggregate intrinsic value represents the difference between the grant price of the award, which is zero, and the closing market price of our common stock on December 31, 2018.

The fair value of restricted stock that vested in the years ended December 31, 2018, 2017 and 2016 totaled $80.4 million, $22.3 million and $7.7 million, respectively.

Income Taxes

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income Taxes

Note 12 — Income Taxes

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

	Year Ended December 31,
	2018		2017			2016
Domestic	$	680,423	$	(97,938	)	$	(155,375	)
Foreign		2,302		1,862			2,727
Income (loss) before provision for income taxes	$	682,725	$	(96,076	)	$	(152,648	)

Provision for Income Taxes

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

	Year Ended December 31,
	2018		2017		2016
Current:
Federal	$	—	$	—	$	—
State		699		1		(1	)
Foreign		620		580		992
Total Current		1,319		581		991
Deferred:
Federal		—		—		—
State		—		—		—
Foreign		93		35		(115	)
Total Deferred		93		35		(115	)
Provision for income taxes	$	1,412	$	616	$	876

Income tax provision related to continuing operations differs from the amount computed by applying the statutory income tax rate of 21% for 2018 and 35% for 2017 and 2016 to pretax income (loss) as follows (in thousands):

	Year Ended December 31,
	2018			2017			2016
Income tax expense (benefit) at federal statutory rate	$	143,372		$	(33,627	)	$	(53,427	)
Non-cash interest expense on liability related to sale of future royalties		4,451			6,604			6,899
Non-deductible officers' compensation		3,182			2,547			220
Tax law changes		45			248,155			—
Stock-based compensation		(66,716	)		(20,665	)		528
Change in valuation allowance		(46,885	)		(186,124	)		51,981
Research credits		(17,295	)		(8,038	)		(4,543	)
Premium on equity issuance		(12,551	)		—			—
Sale of future royalties		(6,995	)		(8,236	)		—
Other		804			—			(782	)
Provision for income taxes	$	1,412		$	616		$	876

Tax Law Changes

The U.S. Tax Cuts and Jobs Act (the Tax Act) was enacted on December 22, 2017. The Tax Act reduces the U.S. federal corporate tax rate from 35% in 2017 to 21% in 2018, requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and creates new taxes on certain foreign sourced earnings. At December 31, 2018, we have completed our accounting for the tax effects of enactment of the Tax Act, which, other than the $248.2 million decrease in the valuation of our federal deferred tax assets shown above, did not have a material effect on our Consolidated Financial Statements.

Deferred Tax Assets and Liabilities

Deferred income taxes reflect the net tax effects of loss and credit carryforwards and temporary differences between the carrying amount of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. We remeasured certain deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, which includes the change in the federal rate to 21% as of December 31, 2017. Significant components of our deferred tax assets for federal and state income taxes are as follows (in thousands):

	December 31,
	2018			2017
Deferred tax assets:
Net operating loss carryforwards	$	300,693		$	364,864
Research and other credits		116,955			94,103
Stock-based compensation		21,518			14,552
Capitalized research expenses		8,072			5,497
Reserves and accruals		8,066			5,659
Deferred revenue		4,467			3,796
Property, plant and equipment		2,124			6,848
Other		(1,270	)		1,156
Deferred tax assets before valuation allowance		460,625			496,475
Valuation allowance for deferred tax assets		(460,455	)		(496,191	)
Total deferred tax assets		170			284
Total deferred tax liabilities		—			—
Net deferred tax assets	$	170		$	284

Realization of our deferred tax assets is dependent upon future earnings, if any, the timing and amount of which are uncertain. Because of our lack of U.S. earnings history, other than income resulting from revenue recognized from the BMS collaboration agreement, and projected future losses, the net U.S. deferred tax assets have been fully offset by a valuation allowance. The valuation allowance decreased by $35.7 million and $169.3 million during the years ended December 31, 2018 and 2017, respectively, and increased by $52.5 million during the year ended December 31, 2016. The decrease in the valuation allowance for the year ended December 31, 2018 reflects the utilization of net operating loss carryforwards to offset federal and state taxable income, and the decrease in the valuation allowance for the year ended December 31, 2017 is primarily due to the change in the federal rate. The valuation allowance includes approximately $35.6 million of income tax benefit at both December 31, 2018 and December 31, 2017 related to stock-based compensation that will be included in income tax expense in our Consolidated Statement of Operations when realized.

For 2017, the one-time transition tax under the Tax Act was based on our total post-1986 earnings and profits (E&P) that we previously deferred from U.S. income taxes. We concluded that there was negative E&P on an aggregate basis and we have not recorded any amount for any one-time transition tax triggered by the Tax Act. No additional income taxes have been provided for any remaining undistributed foreign earnings not subject to the transition tax, or any additional outside basis difference inherent in these entities, as these amounts continue to be indefinitely reinvested in foreign operations.

Net Operating Loss and Tax Credit Carryforwards

As of December 31, 2018, we had a net operating loss carryforward for federal income tax purposes of approximately $1,304.1 million, portions of which will begin to expire in 2022. As of December 31, 2018, we had a total state net operating loss carryforward of approximately $471.1 million, portions of which will begin to expire in 2024. Utilization of some of the federal and state net operating loss and credit carryforwards are subject to annual limitations due to the “change in ownership” provisions of the Internal Revenue Code of 1986 and similar state provisions.

We have federal research credits of approximately $101.0 million, which will begin to expire in 2020 and state research credits of approximately $40.0 million which have no expiration date. We have federal orphan drug credits of $17.7 million which will begin to expire in 2026. These tax credits are subject to the same limitations discussed above.

Unrecognized tax benefits

With the exception of net income recognized in 2018, we have incurred net operating losses since inception. Our policy is to include interest and penalties related to unrecognized tax benefits, if any, within the provision for income taxes in the consolidated statements of operations. If we are eventually able to recognize our uncertain positions, our effective tax rate may be reduced. We currently have a full valuation allowance against our U.S. net deferred tax asset which would impact the timing of the effective tax rate benefit should any of these uncertain tax positions be favorably settled in the future. Adjustments to the substantial majority of our uncertain tax positions would result in an adjustment of our net operating loss or tax credit carry forwards rather than resulting in a cash outlay.

We file income tax returns in the U.S., California, Alabama, certain other states and India. Because of net operating losses and research credit carryovers, substantially all of our domestic tax years remain open and subject to examination. We are currently under examination in India for the fiscal years ending 2009, 2016 and 2017.

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

	December 31,
	2018		2017			2016
Beginning balance	$	20,483	$	18,413		$	17,384
Tax positions related to current year
Additions:
Federal		2,019		1,206			530
State		3,645		1,666			499
Reductions		—		—			—
Tax positions related to prior year
Additions:
Federal		669		—			—
State		603		—			—
Foreign		—		—			—
Reductions				(802	)		—
Settlements		—		—			—
Lapses in statute of limitations		—		—			—
Ending balance	$	27,419	$	20,483		$	18,413

Although it is reasonably possible that certain unrecognized tax benefits may increase or decrease within the next twelve months, we do not anticipate any significant changes to unrecognized tax benefits over the next twelve months. During the years ended December 31, 2018, 2017 and 2016, no significant interest or penalties were recognized relating to unrecognized tax benefits.

Segment Reporting

12 Months Ended

Dec. 31, 2018

Segment Reporting [Abstract]

Segment Reporting

Note 13 — Segment Reporting

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

Our revenue is derived primarily from customers in the pharmaceutical and biotechnology industries. Revenue from BMS represented 89% of our revenue for the year ended December 31, 2018. Revenue from Lilly and UCB represented 42% and 12% of our revenue, respectively, for the year ended December 31, 2017. Revenue from AstraZeneca, UCB, Ophthotech and Roche represented 29%, 21%, 19% and 11% of our revenue, respectively, for the year ended December 31, 2016.

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

	Year Ended December 31,
	2018		2017		2016
United States	$	1,090,794	$	190,810	$	39,147
Europe		102,529		116,901		126,289
Total revenue	$	1,193,323	$	307,711	$	165,436

At December 31, 2018, $42.9 million, or approximately 88%, of the net book value of our property, plant and equipment was located in the United States and $5.9 million, or approximately 12%, was located in India. At December 31, 2017, $41.7 million, or approximately 88%, of the net book value of our property, plant and equipment was located in the United States and $5.8 million, or approximately 12%, was located in India.

Selected Quarterly Financial Data

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data

Note 14 — Selected Quarterly Financial Data (Unaudited)

The following table sets forth certain unaudited quarterly financial data. In our opinion, the unaudited information set forth below has been prepared on the same basis as our audited information and includes all adjustments necessary to present fairly the information set forth herein. We have experienced fluctuations in our quarterly results and expect these fluctuations to continue in the future. Due to these and other factors, we believe that quarter-to-quarter comparisons of our operating results will not be meaningful, and the results for any one quarter may not be indicative of our future performance. We have reclassified certain items previously reported in specific financial statement captions to conform to the current period presentation. Such reclassifications have not materially impacted previously reported total revenues, operating income (loss) or net income (loss). All data is in thousands except per share information.

	Year Ended December 31, 2018											Year Ended December 31, 2017
	Q1			Q2		Q3			Q4			Q1			Q2			Q3		Q4
Product sales	$	6,295		$	5,863	$	4,256		$	4,360		$	4,756		$	15,693		$	4,448	$	7,791
Total revenue	$	38,018		$	1,087,717	$	27,762		$	39,826		$	24,728		$	34,589		$	152,928	$	95,466
Cost of goods sold	$	6,646		$	5,522	$	4,783		$	7,461		$	6,131		$	8,989		$	5,674	$	9,753
Research and development expenses	$	99,424		$	88,334	$	102,895		$	108,883		$	61,058		$	60,260		$	65,714	$	81,429
Operating income (loss)	$	(86,739	)	$	973,600	$	(98,634	)	$	(100,295	)	$	(54,437	)	$	(50,656	)	$	69,485	$	(24,034	)
Net income (loss)	$	(95,792	)	$	971,460	$	(96,143	)	$	(98,212	)	$	(63,866	)	$	(59,871	)	$	60,871	$	(33,826	)
Net income (loss) per share(1)
Basic	$	(0.60	)	$	5.67	$	(0.56	)	$	(0.57	)	$	(0.42	)	$	(0.39	)	$	0.39	$	(0.21	)
Diluted	$	(0.60	)	$	5.33	$	(0.56	)	$	(0.57	)	$	(0.42	)	$	(0.39	)	$	0.37	$	(0.21	)

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

Organization and Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

Organization

Basis of Presentation, Principles of Consolidation and Use of Estimates

Reclassifications

Cash, Cash Equivalents, and Investments, and Fair Value of Financial Instruments

Accounts Receivable and Significant Customer Concentrations

Inventory and Significant Supplier Concentrations

Long-Lived Assets

Collaborative Arrangements

Revenue Recognition

Product sales

Royalty revenue

License, collaboration and other revenue

Shipping and Handling Costs

We recognize costs related to shipping and handling of product to customers in cost of goods sold.

Research and Development Expense

Stock-Based Compensation

Net Income (Loss) Per Share

Income Taxes

Comprehensive income (loss)

Adoption of New Accounting Principle


	As reported			Adjustments			Balances Without the Adoption of Topic 606
Consolidated Balance Sheet data as of December 31, 2018
Accounts receivable, net	$	43,213		$	(21,030	)	$	22,183
Deferred revenue, current portion		13,892			1,191			15,083
Deferred revenue, less current portion		10,744			(112	)		10,632
Accumulated deficit		(1,424,051	)		(22,109	)		(1,446,160	)

Consolidated Statement of Operations data for the year ended December 31, 2018
Product sales	$	20,774		$	(192	)	$	20,582
Royalty revenue		41,976			(286	)		41,690
License, collaboration and other revenue		1,097,265			(8,934	)		1,088,331
Total revenue		1,193,323			(9,412	)		1,183,911

Recent Accounting Pronouncements

We periodically assess the estimated royalty payments to RPI from UCB and Roche and to the extent the amount or timing of such payments is materially different than our original estimates, we will prospectively adjust the amortization of the Royalty Obligation.

Organization and Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2018

ASC 606 [Member]

Impact of Adoption of ASC 606 on Condensed Consolidated Balance Sheet and Condensed Consolidated Statement of Operations

The impact of the adoption of ASC 606 on our Consolidated Balance Sheet as of December 31, 2018 and Consolidated Statement of Operations data for the year ended December 31, 2018 was as follows (in thousands):


	As reported			Adjustments			Balances Without the Adoption of Topic 606
Consolidated Balance Sheet data as of December 31, 2018
Accounts receivable, net	$	43,213		$	(21,030	)	$	22,183
Deferred revenue, current portion		13,892			1,191			15,083
Deferred revenue, less current portion		10,744			(112	)		10,632
Accumulated deficit		(1,424,051	)		(22,109	)		(1,446,160	)

Consolidated Statement of Operations data for the year ended December 31, 2018
Product sales	$	20,774		$	(192	)	$	20,582
Royalty revenue		41,976			(286	)		41,690
License, collaboration and other revenue		1,097,265			(8,934	)		1,088,331
Total revenue		1,193,323			(9,412	)		1,183,911

Cash and Investments in Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2018

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
	December 31, 2018		December 31, 2017
Cash and cash equivalents	$	194,905	$	4,762
Short-term investments		1,140,445		291,370
Long-term investments		582,889		57,088
Total cash and investments in marketable securities	$	1,918,239	$	353,220

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		December 31, 2018		December 31, 2017
Corporate notes and bonds		2	$	1,288,986	$	216,253
Corporate commercial paper		2		498,048		128,096
Obligations of U.S. government agencies		2		12,977		2,977
Available-for-sale investments				1,800,011		347,326
Money market funds		1		105,656		302
Certificate of deposit	N/A			6,760		1,132
Cash	N/A			5,812		4,460
Total cash and investments in marketable securities			$	1,918,239	$	353,220

Inventory (Tables)

12 Months Ended

Dec. 31, 2018

Inventory Disclosure [Abstract]

Inventory

Inventory consists of the following (in thousands):

	December 31,
	2018		2017
Raw materials	$	1,846	$	1,796
Work-in-process		6,403		4,843
Finished goods		3,132		4,087
Total inventory	$	11,381	$	10,726

Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2018

Property Plant And Equipment [Abstract]

Property, Plant and Equipment

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

	December 31,
	2018			2017
Building and leasehold improvements	$	77,771		$	81,444
Laboratory equipment		33,806			31,214
Computers, furniture, and other		31,354			27,800
Manufacturing equipment		21,339			20,695
Depreciable property, plant and equipment at cost		164,270			161,153
Less: accumulated depreciation		(120,507	)		(115,090	)
Depreciable property, plant and equipment, net		43,763			46,063
Construction-in-progress		5,088			1,400
Property, plant and equipment, net	$	48,851		$	47,463

Leases (Tables)

12 Months Ended

Dec. 31, 2018

Leases [Abstract]

Future Minimum Lease Payments for Operating Leases

Our future minimum lease payments for our operating leases at December 31, 2018 are as follows (in thousands):

Year ending December 31,
2019	$	7,914
2020		10,617
2021		13,649
2022		14,117
2023		14,599
2024 and thereafter		98,315
Total future minimum lease payments	$	159,211

Liability Related to the Sale of Future Royalties (Tables)

12 Months Ended

Dec. 31, 2018

Summary of Liability Related to Potential Future Royalties

	Year ended December 31, 2018			Period from inception to December 31, 2018
Liability related to the sale of future royalties—beginning balance	$	96,922		$	—
Proceeds from sale of future royalties		—			124,000
Payments from Nektar to RPI		—			(10,000	)
Non-cash CIMZIA^® and MIRCERA^® royalty revenue		(33,308	)		(170,839	)
Non-cash interest expense recognized		21,196			141,649
Liability related to the sale of future royalties – ending balance		84,810			84,810
Less: unamortized transaction costs		(1,899	)		(1,899	)
Liability related to the sale of future royalties, net	$	82,911		$	82,911

License and Collaboration Agreements (Tables)

12 Months Ended

Dec. 31, 2018

Organization Consolidation And Presentation Of Financial Statements [Abstract]

License, Collaboration and Other Revenue

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

		Year Ended December 31,
Partner	Agreement	2018		2017		2016
Bristol-Myers Squibb	NKTR-214	$	1,059,768	$	—		—
Baxalta Incorporated / Takeda	Hemophilia, including ADYNOVATE^® and ADYNOVI^TM		20,328		11,443		650
Eli Lilly and Company	NKTR-358		11,634		130,087		—
Amgen, Inc.	Neulasta^®		5,000		5,000		5,000
Ophthotech Corporation⁽¹⁾	Fovista^®		—		19,123		1,408
Bayer Healthcare LLC⁽¹⁾	BAY41-6551 (Amikacin Inhale)		—		17,931		1,429
AstraZeneca AB	MOVANTIK^®and MOVENTIG^®		—		4,600		33,000
Other			535		22,781		18,895
License, collaboration and other revenue		$	1,097,265	$	210,965	$	60,382

(1)	These collaboration agreements were completed as of December 31, 2017.

Changes in Deferred Revenue Balance from Collaboration Agreements

The following table presents the changes in our deferred revenue balance from our collaboration agreements during the year ended December 31, 2018 (in thousands):

	For the year ended December 31, 2018
Deferred revenue—December 31, 2017	$	37,970
Transition adjustment related to adoption of ASC 606		(1,953	)
Additions to deferred revenue		5,950
Recognition of previously unearned revenue		(17,331	)
Deferred revenue—December 31, 2018	$	24,636

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2018

Stock-Based Compensation Expense

We issue stock-based awards from our equity incentive plans, which are more fully described in Note 9. Stock-based compensation expense was recognized as follows (in thousands):

	Year Ended December 31,
	2018		2017		2016
Cost of goods sold	$	4,629	$	2,333	$	1,620
Research and development		56,193		21,252		13,093
General and administrative		27,279		13,030		11,137
Total stock-based compensation	$	88,101	$	36,615	$	25,850

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

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

	Year Ended December 31,
	2018			2017			2016
Average risk-free interest rate		2.8	%		2.0	%		1.4	%
Dividend yield		0.0	%		0.0	%		0.0	%
Average volatility factor		61.0	%		54.2	%		51.7	%
Average weighted average expected life	5.1 years			5.3 years			5.3 years

Stock Option Activity Under Equity Incentive Plans

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

	Number of Shares			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Life (in Years)		Aggregate Intrinsic Value(1)
Outstanding at December 31, 2017		18,826		$	20.35
Options granted		1,846			55.35
Options exercised		(4,374	)		13.24
Options forfeited & canceled		(368	)		27.75
Outstanding at December 31, 2018		15,930		$	26.18		4.96	$	214,525

Exercisable at December 31, 2018		9,393			16.16		3.69	$	173,436

(1)	Aggregate intrinsic value represents the difference between the exercise price of the option and the closing market price of our common stock on December 31, 2018.

Restricted Stock Units (RSU) [Member]

Restricted Stock Unit Award Activity

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

	Units Issued			Weighted- Average Grant Date Fair Value		Aggregate Intrinsic Value(1)
Balance at December 31, 2017		2,578		$	35.52
Granted		2,125			41.67
Vested and released		(1,255	)		29.44
Forfeited and canceled		(128	)		40.39
Balance at December 31, 2018		3,320		$	41.57	$	109,125

(1)	Aggregate intrinsic value represents the difference between the grant price of the award, which is zero, and the closing market price of our common stock on December 31, 2018.

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Tax Disclosure [Abstract]

Income (Loss) Before Provision for Income Taxes

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

	Year Ended December 31,
	2018		2017			2016
Domestic	$	680,423	$	(97,938	)	$	(155,375	)
Foreign		2,302		1,862			2,727
Income (loss) before provision for income taxes	$	682,725	$	(96,076	)	$	(152,648	)

Provision for Income Taxes

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

	Year Ended December 31,
	2018		2017		2016
Current:
Federal	$	—	$	—	$	—
State		699		1		(1	)
Foreign		620		580		992
Total Current		1,319		581		991
Deferred:
Federal		—		—		—
State		—		—		—
Foreign		93		35		(115	)
Total Deferred		93		35		(115	)
Provision for income taxes	$	1,412	$	616	$	876

Income Tax Provision Related to Continuing Operations

	Year Ended December 31,
	2018			2017			2016
Income tax expense (benefit) at federal statutory rate	$	143,372		$	(33,627	)	$	(53,427	)
Non-cash interest expense on liability related to sale of future royalties		4,451			6,604			6,899
Non-deductible officers' compensation		3,182			2,547			220
Tax law changes		45			248,155			—
Stock-based compensation		(66,716	)		(20,665	)		528
Change in valuation allowance		(46,885	)		(186,124	)		51,981
Research credits		(17,295	)		(8,038	)		(4,543	)
Premium on equity issuance		(12,551	)		—			—
Sale of future royalties		(6,995	)		(8,236	)		—
Other		804			—			(782	)
Provision for income taxes	$	1,412		$	616		$	876

Significant Components of Deferred Tax Assets and Liabilities

We remeasured certain deferred tax assets and liabilities based on the rates at which they are expected to reverse in the future, which includes the change in the federal rate to 21% as of December 31, 2017. Significant components of our deferred tax assets for federal and state income taxes are as follows (in thousands):

	December 31,
	2018			2017
Deferred tax assets:
Net operating loss carryforwards	$	300,693		$	364,864
Research and other credits		116,955			94,103
Stock-based compensation		21,518			14,552
Capitalized research expenses		8,072			5,497
Reserves and accruals		8,066			5,659
Deferred revenue		4,467			3,796
Property, plant and equipment		2,124			6,848
Other		(1,270	)		1,156
Deferred tax assets before valuation allowance		460,625			496,475
Valuation allowance for deferred tax assets		(460,455	)		(496,191	)
Total deferred tax assets		170			284
Total deferred tax liabilities		—			—
Net deferred tax assets	$	170		$	284

Unrecognized Tax Benefits

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

	December 31,
	2018		2017			2016
Beginning balance	$	20,483	$	18,413		$	17,384
Tax positions related to current year
Additions:
Federal		2,019		1,206			530
State		3,645		1,666			499
Reductions		—		—			—
Tax positions related to prior year
Additions:
Federal		669		—			—
State		603		—			—
Foreign		—		—			—
Reductions				(802	)		—
Settlements		—		—			—
Lapses in statute of limitations		—		—			—
Ending balance	$	27,419	$	20,483		$	18,413

Segment Reporting (Tables)

12 Months Ended

Dec. 31, 2018

Segment Reporting [Abstract]

Revenue by Geographic Area

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

	Year Ended December 31,
	2018		2017		2016
United States	$	1,090,794	$	190,810	$	39,147
Europe		102,529		116,901		126,289
Total revenue	$	1,193,323	$	307,711	$	165,436

Selected Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2018

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Data

	Year Ended December 31, 2018											Year Ended December 31, 2017
	Q1			Q2		Q3			Q4			Q1			Q2			Q3		Q4
Product sales	$	6,295		$	5,863	$	4,256		$	4,360		$	4,756		$	15,693		$	4,448	$	7,791
Total revenue	$	38,018		$	1,087,717	$	27,762		$	39,826		$	24,728		$	34,589		$	152,928	$	95,466
Cost of goods sold	$	6,646		$	5,522	$	4,783		$	7,461		$	6,131		$	8,989		$	5,674	$	9,753
Research and development expenses	$	99,424		$	88,334	$	102,895		$	108,883		$	61,058		$	60,260		$	65,714	$	81,429
Operating income (loss)	$	(86,739	)	$	973,600	$	(98,634	)	$	(100,295	)	$	(54,437	)	$	(50,656	)	$	69,485	$	(24,034	)
Net income (loss)	$	(95,792	)	$	971,460	$	(96,143	)	$	(98,212	)	$	(63,866	)	$	(59,871	)	$	60,871	$	(33,826	)
Net income (loss) per share(1)
Basic	$	(0.60	)	$	5.67	$	(0.56	)	$	(0.57	)	$	(0.42	)	$	(0.39	)	$	0.39	$	(0.21	)
Diluted	$	(0.60	)	$	5.33	$	(0.56	)	$	(0.57	)	$	(0.42	)	$	(0.39	)	$	0.37	$	(0.21	)

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

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands, shares in Millions		3 Months Ended								12 Months Ended
	Jan. 01, 2018 USD ($)	Dec. 31, 2018 USD ($) Customer	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($) Customer	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2018 USD ($) Customer Reporting_Unit shares	Dec. 31, 2017 USD ($) Customer shares	Dec. 31, 2016 USD ($) shares
Organization And Summary Of Significant Accounting Policies [Line Items]
Cash and investments in marketable securities		$ 1,918,239				$ 353,220				$ 1,918,239	$ 353,220
Senior secured notes		$ 250,000								$ 250,000
Senior secured notes, maturity date										Oct. 05, 2020
Contract with customer, asset, reclassified to receivable										$ 24,200	3,300
Net expense reimbursements from collaboration partner										$ 19,000	$ 1,700
Number of customers accounted for major accounts receivable \| Customer		3				4				3	4
Percentage of accounts receivable customers one										44.00%	43.00%
Percentage of accounts receivable customers two										36.00%	20.00%
Percentage of accounts receivable customers three										12.00%	19.00%
Percentage of accounts receivable customers four											14.00%
Number of reporting unit evaluated for goodwill \| Reporting_Unit										1
Customer payment period from receipt of invoice										30 days
Weighted-average of potentially dilutive securities (stock options and RSUs) included in calculation of diluted securities under treasury stock method \| shares										10.5
Minimum percentage of amount realized upon ultimate settlement										50.00%
Revenue recognized from contracts with customers		$ 39,826	$ 27,762	$ 1,087,717	$ 38,018	$ 95,466	$ 152,928	$ 34,589	$ 24,728	$ 1,193,323	$ 307,711	$ 165,436
Deferred rent		9,300				6,000				9,300	6,000
Royalty [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Revenue recognized from contracts with customers										41,976	$ 33,527	$ 19,542
ASC 606 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Adjustment to retained earnings	$ 12,700
Reduction of deferred revenue	(2,000)
ASC 606 [Member] \| MOVANTIK and ADYNOVATE [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Revenue recognized from contracts with customers					$ 11,100	$ 9,600
Type of Revenue [Extensible List]					us-gaap:RoyaltyMember	us-gaap:RoyaltyMember
ASC 606 [Member] \| Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Revenue recognized from contracts with customers										1,183,911
ASC 606 [Member] \| Royalty [Member] \| Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Adjustment to retained earnings	10,700
Revenue recognized from contracts with customers										$ 41,690
ASC 606 [Member] \| Royalty [Member] \| Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| MOVANTIK and ADYNOVATE [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Adjustment to retained earnings	$ 10,700
Stock Options and Restricted Stock Units [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Weighted average antidilutive securities excluded from computation of earnings per share \| shares											20.6	19.9
Shares of Common Stock Underlying Outstanding Stock Options [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Weighted average antidilutive securities excluded from computation of earnings per share \| shares										3.3
Minimum [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Operating Lease, Right-of-Use Asset		87,000								$ 87,000
Operating Lease, Liability		96,000								96,000
Maximum [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Operating Lease, Right-of-Use Asset		97,000								97,000
Operating Lease, Liability		$ 106,000								$ 106,000
Buildings [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives										20 years
Manufacturing Laboratory and Other Equipment [Member] \| Minimum [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives										3 years
Manufacturing Laboratory and Other Equipment [Member] \| Maximum [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives										10 years

Organization and Summary of Significant Accounting Policies - Impact of Adoption of ASC 606 on Condensed Consolidated Balance Sheet and Condensed Consolidated Statement of Operations (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Consolidated Balance Sheet data
Accounts receivable, net	$ 43,213				$ 5,014				$ 43,213	$ 5,014
Deferred revenue, current portion	13,892				18,949				13,892	18,949
Deferred revenue, less current portion	10,744				19,021				10,744	19,021
Accumulated deficit	(1,424,051)				(2,117,941)				(1,424,051)	(2,117,941)
Condensed Consolidated Statement of Operations data
Total revenue	39,826	$ 27,762	$ 1,087,717	$ 38,018	95,466	$ 152,928	$ 34,589	$ 24,728	1,193,323	307,711	$ 165,436
Product Sales [Member]
Condensed Consolidated Statement of Operations data
Total revenue	4,360	$ 4,256	$ 5,863	$ 6,295	$ 7,791	$ 4,448	$ 15,693	$ 4,756	20,774	32,688	55,354
Royalty [Member]
Condensed Consolidated Statement of Operations data
Total revenue									41,976	33,527	19,542
License, Collaboration and Other Revenue [Member]
Condensed Consolidated Statement of Operations data
Total revenue									1,097,265	$ 210,965	$ 60,382
ASC 606 [Member] \| Adjustments [Member]
Condensed Consolidated Balance Sheet data
Accounts receivable, net	(21,030)								(21,030)
Deferred revenue, current portion	1,191								1,191
Deferred revenue, less current portion	(112)								(112)
Accumulated deficit	(22,109)								(22,109)
Condensed Consolidated Statement of Operations data
Total revenue									(9,412)
ASC 606 [Member] \| Adjustments [Member] \| Product Sales [Member]
Condensed Consolidated Statement of Operations data
Total revenue									(192)
ASC 606 [Member] \| Adjustments [Member] \| Royalty [Member]
Condensed Consolidated Statement of Operations data
Total revenue									(286)
ASC 606 [Member] \| Adjustments [Member] \| License, Collaboration and Other Revenue [Member]
Condensed Consolidated Statement of Operations data
Total revenue									(8,934)
ASC 606 [Member] \| Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Condensed Consolidated Balance Sheet data
Accounts receivable, net	22,183								22,183
Deferred revenue, current portion	15,083								15,083
Deferred revenue, less current portion	10,632								10,632
Accumulated deficit	$ (1,446,160)								(1,446,160)
Condensed Consolidated Statement of Operations data
Total revenue									1,183,911
ASC 606 [Member] \| Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Product Sales [Member]
Condensed Consolidated Statement of Operations data
Total revenue									20,582
ASC 606 [Member] \| Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| Royalty [Member]
Condensed Consolidated Statement of Operations data
Total revenue									41,690
ASC 606 [Member] \| Calculated under Revenue Guidance in Effect before Topic 606 [Member] \| License, Collaboration and Other Revenue [Member]
Condensed Consolidated Statement of Operations data
Total revenue									$ 1,088,331

Cash and Investments in Marketable Securities - Cash and Investments in Marketable Securities, Including Cash Equivalents (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	$ 194,905	$ 4,762
Short-term investments	1,140,445	291,370
Long-term investments	582,889	57,088
Total cash and investments in marketable securities	$ 1,918,239	$ 353,220

Cash and Investments in Marketable Securities - Additional Information (Detail) - USD ($)		12 Months Ended
	Oct. 05, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash and Investments in Marketable Securities [Line Items]
Maximum maturity term for debt securities investment		Two years or less
Weighted average maturity term for debt securities investment		One year or less
Available-for-sale securities, sold		$ 12,000,000	$ 37,500,000	$ 5,000,000
Senior secured notes, maturity date		Oct. 05, 2020
Level 1 to level 2 transfers		$ 0	0
Level 2 to level 1 transfers		0	0
Letter of credit		$ 6,600,000	$ 1,100,000
Senior Notes [Member] \| 7.75% Senior Secured Notes Due October 2020 [Member]
Cash and Investments in Marketable Securities [Line Items]
Senior secured notes, interest rate	7.75%
Senior secured notes, maturity date	Oct. 05, 2020
Minimum cash and investments in marketable securities to be maintained	$ 60,000,000

Cash and Investments in Marketable Securities - Portfolio of Cash and Investments in Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	$ 1,800,011	$ 347,326
Cash	5,812	4,460
Total cash and investments in marketable securities	1,918,239	353,220
Corporate Commercial Paper [Member] \| Fair Value Hierarchy Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	498,048	128,096
Corporate Notes and Bonds [Member] \| Fair Value Hierarchy Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	1,288,986	216,253
Obligations of U.S. government agencies [Member] \| Fair Value Hierarchy Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	12,977	2,977
Money Market Funds [Member] \| Fair Value Hierarchy Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	105,656	302
Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	$ 6,760	$ 1,132

Inventory - Inventory (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 1,846	$ 1,796
Work-in-process	6,403	4,843
Finished goods	3,132	4,087
Total inventory	$ 11,381	$ 10,726

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciable property and equipment at cost	$ 164,270	$ 161,153
Less: accumulated depreciation	(120,507)	(115,090)
Depreciable property, plant and equipment, net	43,763	46,063
Construction-in-progress	5,088	1,400
Property plant and equipment, net	48,851	47,463
Building and Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Depreciable property and equipment at cost	77,771	81,444
Manufacturing Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciable property and equipment at cost	21,339	20,695
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciable property and equipment at cost	33,806	31,214
Computers Furniture and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciable property and equipment at cost	$ 31,354	$ 27,800

Property, Plant and Equipment - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciation and amortization expenses		$ 8.8	$ 12.6	$ 13.2
Costs related to terminated manufacturing obligations	$ 0.9
Manufacturing Equipment [Member]
Property, Plant and Equipment [Line Items]
Original cost of impaired equipment	23.4		23.4
Net book value of impaired equipment	$ 15.1		$ 15.1

Senior Secured Notes - Additional Information (Detail) - USD ($)		12 Months Ended
	Oct. 05, 2015	Dec. 31, 2018
Secured Notes [Line Items]
Senior secured notes, principal amount		$ 250,000,000
Actual days outstanding		360 days
Senior secured notes, maturity date		Oct. 05, 2020
Senior Notes [Member] \| 7.75% Senior Secured Notes Due October 2020 [Member]
Secured Notes [Line Items]
Senior secured notes, principal amount	$ 250,000,000
Senior secured notes, interest rate	7.75%
Senior secured notes, maturity date	Oct. 05, 2020
Frequency of payment		Quarterly
Issuance costs	$ 8,900,000
Debt discount on transaction and facility fees	8,700,000
Unamortized debt discount and issuance costs		$ 3,100,000
Minimum cash and investments in marketable securities to be maintained	$ 60,000,000
Percentage of repurchase of notes on principal amount of notes	101.00%
Percentage of repurchase of notes on principal amount of notes upon sale of assets	100.00%
Senior Notes [Member] \| 7.75% Senior Secured Notes Due October 2020 [Member] \| Level 3 [Member]
Secured Notes [Line Items]
Senior notes fair value		$ 258,000,000
Senior Notes [Member] \| 7.75% Senior Secured Notes Redemption Date Before October 5, 2019 [Member]
Secured Notes [Line Items]
Debt redemption price percentage of principal amount	102.00%
Senior Notes [Member] \| 7.75% Senior Secured Notes Redemption Date After October 5, 2019 [Member]
Secured Notes [Line Items]
Debt redemption price percentage of principal amount	100.00%

Leases - Additional Information (Detail) $ in Millions	1 Months Ended				12 Months Ended
Leases - Additional Information (Detail) $ in Millions	Dec. 31, 2018 USD ($) ft² Space	Jun. 30, 2018 ft²	May 31, 2018 ft²	Aug. 31, 2017 ft² yr	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Leases [Line Items]
Rent expense \| $					$ 8.1	$ 4.7	$ 3.2
Deferred rent \| $	$ 9.3				$ 9.3	$ 6.0
ARE-San Francisco No. 19, LLC [Member] \| Mission Bay Lease [Member]
Leases [Line Items]
Extended lease term start year				2020
Lease expiration year				2030
Lease space				134,356
Lease, option to extend, description					The term of the Mission Bay Lease commenced on September 1, 2017, and will expire January 31, 2030, subject to our right to extend the term of the lease for two consecutive five-year periods.
Number of consecutive 5 year terms to extend lease \| yr				2
Lease extension term				5 years
Lease commencement date				Sep. 01, 2017
Lease expiration date				Jan. 31, 2030
Additional space required to be leased in the future				18,000
Kilroy Realty Finance Partnership, L.P [Member] \| Third Street Lease [Member]
Leases [Line Items]
Lease space			135,936
Lease, option to extend, description					The lease term includes a right to extend the term for a consecutive five-year period.
Lease extension term			5 years
Lease expiration date			Jan. 31, 2030
Lease term start month and year			2018-06
Leased space delivered	67,105	1,726
Number of additional spaces delivered \| Space	2
Remaining square feet of space expected delivery year			2019

Leases - Future Minimum Lease Payments for Operating Leases (Detail) $ in Thousands	Dec. 31, 2018 USD ($)
Leases [Abstract]
2019	$ 7,914
2020	10,617
2021	13,649
2022	14,117
2023	14,599
2024 and thereafter	98,315
Total future minimum lease payments	$ 159,211

Liability Related to the Sale of Future Royalties - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended		3 Months Ended		12 Months Ended			70 Months Ended	82 Months Ended
	Feb. 24, 2012	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2018
Liability Related to the Sale of Future Royalties [Line Items]
Royalty agreement contingent payment description						As a result of worldwide net sales of MIRCERA® for the 12 month periods ended December 31, 2013 and 2012 not reaching certain minimum thresholds.
Non-cash royalty revenue related to sale of future royalties						$ 33,308	$ 30,531	$ 30,158		$ 170,839
Non-cash interest expense on liability related to sale of future royalties						$ 21,196	$ 18,869	$ 19,712		$ 141,649
Annual interest rate				18.70%	17.60%				17.00%
Prospective interest rate				29.00%	21.00%
Purchase and Sale Agreement with RPI [Member]
Liability Related to the Sale of Future Royalties [Line Items]
Proceeds from sale of royalty rights	$ 124,000
Transaction costs related to sale of potential future royalties	$ 4,400
Payment made for milestone not achieved year two		$ 7,000
Payment made for milestone not achieved year one			$ 3,000

Liability Related to the Sale of Future Royalties - Summary of Liability Related to Potential Future Royalties (Detail) - USD ($) $ in Thousands	12 Months Ended			82 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Other Liabilities Disclosure [Abstract]
Liability related to the sale of future royalties—beginning balance	$ 96,922			$ 0
Proceeds from sale of future royalties	0			124,000
Payments from Nektar to RPI	0			(10,000)
Non-cash CIMZIA® and MIRCERA® royalty revenue	(33,308)	$ (30,531)	$ (30,158)	(170,839)
Non-cash interest expense recognized	21,196	18,869	$ 19,712	141,649
Liability related to the sale of future royalties – ending balance	84,810	96,922		84,810
Less: unamortized transaction costs	(1,899)			(1,899)
Liability related to the sale of future royalties, net	$ 82,911	$ 94,655		$ 82,911

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Loss Contingencies [Line Items]
Purchase commitments related to contract manufacturing, clinical development and certain other items	$ 63,300,000
Putative Securities Class Action [Member]
Loss Contingencies [Line Items]
Litigation matters, liabilities	0
Indemnification Obligation [Member]
Loss Contingencies [Line Items]
Litigation matters, liabilities	0	$ 0
Merger and Acquisition Related Claims [Member] \| Maximum [Member]
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	2,500,000
Securities Related Claims [Member]
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	2,500,000
Non-Securities Related Claims [Member]
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	$ 1,250,000

Stockholders' Equity - Additional Information (Detail) - USD ($)				12 Months Ended
	Jun. 26, 2018	Apr. 03, 2018	Oct. 24, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class of Stock [Line Items]
Proceeds from sale of common stock			$ 189,700,000
Stock issued during period subject to lock-up and stand-still provisions period		5 years
Number of shares to be issued upon exercise of outstanding options or vesting of RSUs				19,250,000
Number of shares available for issuance under equity compensation plans				12,690,000
Common stock, shares authorized				300,000,000	300,000,000
Maximum 401(k) per employee, percentage of annual salary				60.00%
Matching 401(k) employer contribution, maximum amount				$ 6,000
Compensation expense in connection with 401(k) retirement plan				$ 2,800,000	$ 1,600,000	$ 1,100,000
Change in control severance payment period for executives				12 months
Change in control severance payment period for employees				6 months
Change in control cash severance payment for chief executive officer				24 months base salary plus annual target incentive pay
Employee Stock Purchase Plan [Member]
Class of Stock [Line Items]
Common stock, shares authorized				2,500,000
Percentage of purchase price of stock				85.00%
2017 Performance Incentive Plan [Member]
Class of Stock [Line Items]
Number of common stock shares available for stock options grants				8,300,000
Number of additional shares available for award grants	10,900,000
Share-based compensation plan's share limit reduction for every one restricted stock unit granted				1.5
Stock options term under equity incentive plans				8 years
2017 Performance Incentive Plan [Member] \| Shares of Common Stock Underlying Outstanding Stock Options [Member] \| Employee [Member]
Class of Stock [Line Items]
Service period for stock-based compensation award granted				4 years
2017 Performance Incentive Plan [Member] \| Shares of Common Stock Underlying Outstanding Stock Options [Member] \| Director [Member]
Class of Stock [Line Items]
Service period for stock-based compensation award granted				1 year
2017 Performance Incentive Plan [Member] \| Restricted Stock Units (RSU) [Member] \| Employee [Member]
Class of Stock [Line Items]
Service period for stock-based compensation award granted				3 years
2017 Performance Incentive Plan [Member] \| Restricted Stock Units (RSU) [Member] \| Director [Member]
Class of Stock [Line Items]
Service period for stock-based compensation award granted				1 year
Common Shares [Member]
Class of Stock [Line Items]
Sale of common stock, Shares		8,284,600	14,950,000			14,950,000
Underwriting commissions and discounts			$ 12,100,000
Legal, accounting fees, filing fees and other offering expenses			$ 400,000
Common stock, shares reserved for issuance in equity compensation plans				31,940,416

License and Collaboration Agreements - Additional Information (Detail) - USD ($)			1 Months Ended							3 Months Ended									9 Months Ended	12 Months Ended
	Feb. 13, 2018	Aug. 23, 2017	Apr. 30, 2018	Nov. 30, 2017	Sep. 30, 2017	Jan. 31, 2017	Sep. 30, 2016	Mar. 31, 2016	Jun. 30, 2014	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2010	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2007
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized in period related to performance in prior periods																				$ 95,300,000
Potential future additional payments for development milestones																				1,700,000,000
Deferred revenue, current portion										$ 13,892,000				$ 18,949,000						13,892,000	$ 18,949,000
Deferred revenue, less current portion										10,744,000				19,021,000						10,744,000	19,021,000
Accounts receivable										43,213,000				5,014,000						43,213,000	5,014,000
Development milestones received																				17,331,000
Deferred revenue										24,636,000				37,970,000						24,636,000	37,970,000
Revenue recognized from contracts with customers										39,826,000	$ 27,762,000	$ 1,087,717,000	$ 38,018,000	95,466,000	$ 152,928,000	$ 34,589,000	$ 24,728,000			1,193,323,000	307,711,000	$ 165,436,000
NKTR-214 [Member] \| Nektar's [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront and milestone payments received from license agreements			$ 1,000,000,000
NKTR-214 [Member] \| Nektar's [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum total additional cash payments receivable upon achievement of certain development and regulatory milestones			1,400,000,000
Eligible additional cash payments receivable upon achievement of certain sales milestones			$ 350,000,000
ADYNOVATE [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Sales milestone revenue																				10,000,000
BMS Collaboration Agreement [Member] \| NKTR-214 [Member] \| Nektar's [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Global commercialization profits and losses sharing percentage	65.00%
Percentage of sharing production costs	65.00%
BMS Collaboration Agreement [Member] \| NKTR-214 [Member] \| Nektar's [Member] \| Opdivo [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	32.50%
BMS Collaboration Agreement [Member] \| NKTR-214 [Member] \| Nektar's [Member] \| Opdivo and Yervoy [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	22.00%
NKTR-358 [Member] \| Nektar's [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue										8,300,000										$ 8,300,000
Received upfront and milestone payment					$ 150,000,000
Percentage of sharing in Phase 2 development costs		25.00%
Regulatory milestones payment, description																				A portion of the development milestones may be reduced by 50% under certain conditions, related to the final formulation of the approved product and the timing of prior approval (if any) of competitive products with a similar mechanism of action, which could reduce these milestone payments by 75% if both conditions occur.
AstraZeneca-Kirin [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of upfront payment, market access milestones, royalties and sales milestones								40.00%
Baxalta Incorporated/Takeda [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential future additional payments for development milestones																				$ 10,000,000
Baxalta Incorporated/Takeda [Member] \| Hemophilia
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received under right to sublicense agreement				$ 12,000,000
Baxalta Incorporated/Takeda [Member] \| Hemophilia \| ASC 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue										800,000										800,000
Receivables from customer contracts										15,400,000										15,400,000
Baxalta Incorporated/Takeda [Member] \| Hemophilia \| European Union [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Upfront and milestone payments received from license agreements																				10,000,000
Additional upfront and milestone payments recognized from license agreements										10,000,000
Baxalta Incorporated/Takeda [Member] \| Hemophilia \| European Union [Member] \| ASC 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development milestones received																				10,000,000
Bristol-Myers Squibb [Member] \| Purchase Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Shares issued			8,284,600
Sale of stock consideration received			$ 850,000,000
Bristol-Myers Squibb [Member] \| NKTR-214 [Member] \| Research and Development Expense [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Reimbursement of expenses																				62,500,000	7,800,000
Bristol-Myers Squibb [Member] \| BMS Collaboration Agreement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Accounts receivable										19,000,000										19,000,000
Bristol-Myers Squibb [Member] \| BMS Collaboration Agreement [Member] \| Purchase Agreement [Member]
Collaborative Arrangements And Noncollaborative 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			$ 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 [Member] \| BMS Collaboration Agreement [Member] \| NKTR-214 [Member]
Collaborative Arrangements And Noncollaborative 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 [Member] \| BMS Collaboration Agreement [Member] \| NKTR-214 [Member] \| Opdivo [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	67.50%
Bristol-Myers Squibb [Member] \| BMS Collaboration Agreement [Member] \| NKTR-214 [Member] \| Opdivo and Yervoy [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of sharing development costs	78.00%
Bristol-Myers Squibb [Member] \| Clinical Trial Agreement [Member] \| NKTR-214 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of out-of-pocket costs to be reimbursed by partner							50.00%
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| Phase 1 Clinical Development [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment					17,600,000
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| Drug Product Development [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment					6,500,000
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential future additional development and regulatory milestones		$ 250,000,000
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| Nektar's [Member]
Collaborative Arrangements And Noncollaborative 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 [Member] \| NKTR-358 [Member] \| Nektar's [Member] \| Maximum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of funding phase 3 development costs on an indication by indication basis borne		25.00%
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| Nektar's [Member] \| Minimum [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of funding phase 3 development costs on an indication by indication basis borne		0.00%
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| License [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment					$ 125,900,000
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| License [Member] \| ASC 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Revenue recognized from contracts with customers															$ 125,900,000				$ 125,900,000
Eli Lilly [Member] \| NKTR-358 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of sharing in Phase 2 development costs		75.00%
Amgen, Inc. [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment																		$ 50,000,000
Amgen, Inc. [Member] \| ASC 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue										9,200,000										9,200,000
Ophthotech Corporation [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Advance payment from collaboration partner						$ 12,700,000
Ophthotech Corporation [Member] \| Reagent Shipments [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Advance payment from collaboration partner for reagent shipments						$ 10,400,000
Ophthotech Corporation [Member] \| Minimum Purchase Requirement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Advance payment from collaboration partner																					2,300,000
Ophthotech Corporation [Member] \| Fovista [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Recognition of remaining deferred revenue														18,000,000
Ophthotech Corporation [Member] \| Fovista [Member] \| Novartis Pharma AG [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment									$ 19,800,000
Bayer Healthcare LLC [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment																									$ 40,000,000
Bayer Healthcare LLC [Member] \| Performance-based Milestone Payments [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment																								$ 30,000,000
Recognition of remaining deferred revenue														$ 16,800,000
AstraZeneca AB [Member] \| MOVANTIK and MOVENTIG [Member] \| Upfront Payment Arrangement [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Received upfront and milestone payment																							$ 385,000,000
AstraZeneca AB [Member] \| AstraZeneca-Kirin [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue										0										0
Received upfront and milestone payment																					$ 4,600,000	$ 33,000,000
Percentage of upfront payment, market access milestone payments, royalties and sales milestone payments from sublicense agreement retained by our collaboration partner								60.00%
Other [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential future additional payments for development milestones																				45,500,000
Deferred revenue										$ 6,400,000										$ 6,400,000

License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 1,097,265	$ 210,965	$ 60,382
Bristol-Myers Squibb [Member] \| NKTR-214 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,059,768	0	0
Eli Lilly and Company [Member] \| NKTR-358 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	11,634	130,087	0
Baxalta Incorporated/Takeda [Member] \| Hemophilia, Including ADYNOVATE and ADYNOVITM [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	20,328	11,443	650
Ophthotech Corporation [Member] \| Fovista [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	19,123	1,408
Bayer Healthcare LLC [Member] \| BAY41-6551 (Amikacin Inhale) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	17,931	1,429
Amgen, Inc. [Member] \| Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	5,000	5,000	5,000
AstraZeneca AB [Member] \| MOVANTIK and MOVENTIG [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	4,600	33,000
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 535	$ 22,781	$ 18,895

License and Collaboration Agreements - Changes in Deferred Revenue Balance from Collaboration Agreements (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2018
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Deferred revenue, Beginning balance	$ 37,970
Additions to deferred revenue	5,950
Recognition of previously unearned revenue	(17,331)
Deferred revenue, Ending balance	$ 24,636
ASC 606 [Member]
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Transition adjustment related to adoption of ASC 606		$ (1,953)

Stock-Based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 88,101	$ 36,615	$ 25,850
Cost of Goods Sold [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	4,629	2,333	1,620
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	56,193	21,252	13,093
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 27,279	$ 13,030	$ 11,137

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation costs	$ 258.4
Recognized over a weighted-average period	1 year 10 months 24 days
Dividend yield	0.00%	0.00%	0.00%
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%
Weighted-average grant-date fair value	$ 29.86	$ 20.08	$ 6.54
Total intrinsic value of options exercised	$ 303.4	$ 84.0	$ 17.9
Estimated fair value of options vested	39.0	19.3	16.7
Restricted Stock Units (RSU) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock vested	$ 80.4	$ 22.3	$ 7.7

Stock-Based Compensation - Black-Scholes Option-Pricing Model Assumptions Used to Calculate Fair Value of Employee Stock Options (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Average risk-free interest rate	2.80%	2.00%	1.40%
Dividend yield	0.00%	0.00%	0.00%
Average volatility factor	61.00%	54.20%	51.70%
Average weighted average expected life	5 years 1 month 6 days	5 years 3 months 18 days	5 years 3 months 18 days

Stock-Based Compensation - Stock Option Activity Under Equity Incentive Plans (Detail) - Stock Options [Member] $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding, Beginning balance \| shares	18,826
Number of Shares, Options granted \| shares	1,846
Number of Shares, Options exercised \| shares	(4,374)
Number of Shares, Options forfeited and canceled \| shares	(368)
Number of Shares, Outstanding, Ending balance \| shares	15,930
Number of Shares, Exercisable \| shares	9,393
Weighted-Average Exercise Price per Share, Outstanding, Beginning balance \| $ / shares	$ 20.35
Weighted-Average Exercise Price per Share, Options granted \| $ / shares	55.35
Weighted-Average Exercise Price per Share, Options exercised \| $ / shares	13.24
Weighted-Average Exercise Price per Share, Options forfeited and Canceled \| $ / shares	27.75
Weighted-Average Exercise Price per Share, Outstanding, Ending balance \| $ / shares	26.18
Weighted-Average Exercise Price per Share, Exercisable \| $ / shares	$ 16.16
Weighted-Average Remaining Contractual Life, Outstanding	4 years 11 months 15 days
Weighted-Average Remaining Contractual Life, Exercisable	3 years 8 months 8 days
Aggregate Intrinsic Value, Outstanding \| $	$ 214,525
Aggregate Intrinsic Value, Exercisable \| $	$ 173,436

Stock-Based Compensation - Restricted Stock Unit Award Activity (Detail) - Restricted Stock Units (RSU) [Member] $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units Issued, Beginning balance \| shares	2,578
Granted \| shares	2,125
Vested and released \| shares	(1,255)
Forfeited and canceled \| shares	(128)
Units Issued, Ending balance \| shares	3,320
Weighted Average Grant Date Fair Value, Beginning balance \| $ / shares	$ 35.52
Weighted Average Grant Date Fair Value, Granted \| $ / shares	41.67
Weighted Average Grant Date Fair Value, Vested and released \| $ / shares	29.44
Weighted Average Grant Date Fair Value, Forfeited and canceled \| $ / shares	40.39
Weighted Average Grant Date Fair Value, Ending balance \| $ / shares	$ 41.57
Aggregate Intrinsic Value, Ending balance \| $	$ 109,125

Income Taxes - Income (Loss) Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Domestic	$ 680,423	$ (97,938)	$ (155,375)
Foreign	2,302	1,862	2,727
Income (loss) before provision for income taxes	$ 682,725	$ (96,076)	$ (152,648)

Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal	$ 0	$ 0	$ 0
State	699	1	(1)
Foreign	620	580	992
Total Current	1,319	581	991
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	93	35	(115)
Total Deferred	93	35	(115)
Provision for income taxes	$ 1,412	$ 616	$ 876

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes Disclosure [Line Items]
Statutory income tax rate	21.00%	35.00%	35.00%
Valuation allowance, deferred tax asset, increase (decrease), amount		$ (248,200,000)
Valuation allowance, increase (decrease) amount	$ (35,700,000)	(169,300,000)	$ 52,500,000
Valuation allowance related to stock-based compensation included in income tax expense	(35,600,000)	(35,600,000)
Additional income taxes for remaining undistributed foreign earnings	0
Income tax research credits	17,295,000	8,038,000	4,543,000
Federal orphan drug credits	$ 17,700,000
Federal orphan drug credits, expiration year	2026
Unrecognized tax benefits, period may increase or decrease due to tax examination	Next twelve months
Unrecognized tax benefits, interest recognized	$ 0	0	0
Unrecognized tax benefits, penalties recognized	0	$ 0	$ 0
Federal [Member]
Income Taxes Disclosure [Line Items]
Net operating loss carryforward for income tax	$ 1,304,100,000
Net operating loss carryforward, expiration year	2022
Income tax research credits	$ 101,000,000
Income tax research credits, expiration year	2020
State [Member]
Income Taxes Disclosure [Line Items]
Net operating loss carryforward for income tax	$ 471,100,000
Net operating loss carryforward, expiration year	2024
Income tax research credits	$ 40,000,000

Income Taxes - Income Tax Provision Related to Continuing Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income tax expense (benefit) at federal statutory rate	$ 143,372	$ (33,627)	$ (53,427)
Non-cash interest expense on liability related to sale of future royalties	4,451	6,604	6,899
Non-deductible officers' compensation	3,182	2,547	220
Tax law changes	45	248,155	0
Stock-based compensation	(66,716)	(20,665)	528
Change in valuation allowance	(46,885)	(186,124)	51,981
Research credits	(17,295)	(8,038)	(4,543)
Premium on equity issuance	(12,551)	0	0
Sale of future royalties	(6,995)	(8,236)	0
Other	804	0	(782)
Provision for income taxes	$ 1,412	$ 616	$ 876

Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Net operating loss carryforwards	$ 300,693	$ 364,864
Research and other credits	116,955	94,103
Stock-based compensation	21,518	14,552
Capitalized research expenses	8,072	5,497
Reserves and accruals	8,066	5,659
Deferred revenue	4,467	3,796
Property, plant and equipment	2,124	6,848
Other	(1,270)	1,156
Deferred tax assets before valuation allowance	460,625	496,475
Valuation allowance for deferred tax assets	(460,455)	(496,191)
Total deferred tax assets	170	284
Total deferred tax liabilities	0	0
Net deferred tax assets	$ 170	$ 284

Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Beginning balance	$ 20,483	$ 18,413	$ 17,384
Reductions	0	0	0
Reductions	0	(802)	0
Settlements	0	0	0
Lapses in statute of limitations	0	0	0
Ending balance	27,419	20,483	18,413
Federal [Member]
Income Tax Contingency [Line Items]
Tax positions related to current year, Additions	2,019	1,206	530
Tax positions related to prior year, Additions	669	0	0
State [Member]
Income Tax Contingency [Line Items]
Tax positions related to current year, Additions	3,645	1,666	499
Tax positions related to prior year, Additions	603	0	0
Foreign [Member]
Income Tax Contingency [Line Items]
Tax positions related to prior year, Additions	$ 0	$ 0	$ 0

Segment Reporting - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) Segment	Dec. 31, 2017 USD ($)	Dec. 31, 2016
Segment Reporting Information [Line Items]
Number of operating business segment \| Segment	1
Property, plant and equipment, net	$ 48,851	$ 47,463
United States [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 42,900	$ 41,700
Percentage of net book value of property and equipment	88.00%	88.00%
India [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 5,900	$ 5,800
Percentage of net book value of property and equipment	12.00%	12.00%
Revenue [Member] \| BMS \| Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage revenue from customers	89.00%
Revenue [Member] \| Eli Lilly & Co [Member] \| Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage revenue from customers		42.00%
Revenue [Member] \| UCB [Member] \| Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage revenue from customers		12.00%	21.00%
Revenue [Member] \| AstraZeneca [Member] \| Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage revenue from customers			29.00%
Revenue [Member] \| Ophthotech Corporation [Member] \| Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage revenue from customers			19.00%
Revenue [Member] \| Roche [Member] \| Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage revenue from customers			11.00%

Segment Reporting - Revenue by Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue by geographic area
Total revenue	$ 39,826	$ 27,762	$ 1,087,717	$ 38,018	$ 95,466	$ 152,928	$ 34,589	$ 24,728	$ 1,193,323	$ 307,711	$ 165,436
United States [Member] \| Reportable Geographical Components [Member]
Revenue by geographic area
Total revenue									1,090,794	190,810	39,147
European [Member] \| Reportable Geographical Components [Member]
Revenue by geographic area
Total revenue									$ 102,529	$ 116,901	$ 126,289

Selected Quarterly Financial Data - Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Selected Quarterly Financial Data [Line Items]
Total revenue	$ 39,826	$ 27,762	$ 1,087,717	$ 38,018	$ 95,466	$ 152,928	$ 34,589	$ 24,728	$ 1,193,323	$ 307,711	$ 165,436
Cost of goods sold	7,461	4,783	5,522	6,646	9,753	5,674	8,989	6,131	24,412	30,547	30,215
Research and development expenses	108,883	102,895	88,334	99,424	81,429	65,714	60,260	61,058	399,536	268,461	203,801
Operating income (loss)	(100,295)	(98,634)	973,600	(86,739)	(24,034)	69,485	(50,656)	(54,437)	687,932	(59,642)	(112,855)
Net income (loss)	$ (98,212)	$ (96,143)	$ 971,460	$ (95,792)	$ (33,826)	$ 60,871	$ (59,871)	$ (63,866)	$ 681,313	$ (96,692)	$ (153,524)
Net income (loss) per share
Basic	$ (0.57)	$ (0.56)	$ 5.67	$ (0.60)	$ (0.21)	$ 0.39	$ (0.39)	$ (0.42)	$ 4.02	$ (0.62)	$ (1.10)
Diluted	$ (0.57)	$ (0.56)	$ 5.33	$ (0.60)	$ (0.21)	$ 0.37	$ (0.39)	$ (0.42)	$ 3.78	$ (0.62)	$ (1.10)
Product Sales [Member]
Selected Quarterly Financial Data [Line Items]
Total revenue	$ 4,360	$ 4,256	$ 5,863	$ 6,295	$ 7,791	$ 4,448	$ 15,693	$ 4,756	$ 20,774	$ 32,688	$ 55,354

Consolidated Statements of Stockholders' Equity (Parenthetical) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($)
Statement Of Stockholders Equity [Abstract]
Stock issuance costs	$ 439

License and Collaboration Agreements - License, Collaboration and Other Revenue (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2018
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Collaboration agreements completion date	Dec. 31, 2017

Stock-Based Compensation - Restricted Stock Unit Award Activity (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2018 $ / shares
Restricted Stock Units (RSU) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant price of the award	$ 0