Nektar Therapeutics (NKTR) 10-K 28 Feb 20 2019 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2019	Feb. 19, 2020	Jun. 28, 2019
Document And Entity Information [Abstract]
Title of 12(b) Security	Common Stock, $0.0001 par value
Entity Incorporation, State or Country Code	DE
Document Annual Report	true
Document Transition Report	false
Entity File Number	0-24006
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
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		177,557,144
Entity Public Float			$ 6,184,040,785
Entity Tax Identification Number	94-3134940
Entity Address, Address Line One	455 Mission Bay Boulevard South
Entity Address, City or Town	San Francisco
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94158
City Area Code	415
Local Phone Number	482-5300
Security Exchange Name	NASDAQ
Entity Interactive Data Current	Yes
Documents Incorporated by Reference [Text Block]	Portions of registrant’s definitive Proxy Statement to be filed for its 2019 Annual Meeting of Stockholders are incorporated by reference into Part III hereof. Such Proxy Statement will be filed with the Securities and Exchange Commission within 120 days of the end of the fiscal year covered by this Annual Report on Form 10-K.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 96,363	$ 194,905
Short-term investments	1,228,499	1,140,445
Accounts receivable	36,802	43,213
Inventory	12,665	11,381
Advance payments to contract manufacturers	31,834	26,450
Other current assets	15,387	21,293
Total current assets	1,421,550	1,437,687
Long-term investments	279,119	582,889
Property, plant and equipment, net	64,999	48,851
Operating lease right-of-use assets	134,177	0
Goodwill	76,501	76,501
Other assets	1,010	4,244
Other assets	1,977,356	2,150,172
LIABILITIES AND STOCKHOLDERS’ EQUITY
Accounts payable	19,234	5,854
Accrued compensation	11,467	9,937
Accrued clinical trial expenses	32,626	14,700
Accrued contract manufacturing expenses	7,304	23,841
Other accrued expenses	11,414	9,087
Senior secured notes, net	248,693	0
Interest payable	4,198	4,198
Lease liability, current portion	12,516	0
Deferred revenue, current portion	5,517	13,892
Other current liabilities	924	493
Total current liabilities	353,893	82,002
Senior secured notes, net	0	246,950
Lease liability, less current portion	142,730	0
Liability related to the sale of future royalties, net	72,020	82,911
Deferred revenue, less current portion	2,554	10,744
Other long-term liabilities	768	9,990
Total liabilities	571,965	432,597
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares designated, issued or outstanding at December 31, 2019 or 2018	0	0
Common stock, $0.0001 par value; 300,000 shares authorized; 176,505 shares and 173,530 shares issued and outstanding at December 31, 2019 and 2018, respectively	17	17
Capital in excess of par value	3,271,097	3,147,925
Accumulated other comprehensive loss	(1,005)	(6,316)
Accumulated deficit	(1,864,718)	(1,424,051)
Total stockholders’ equity	1,405,391	1,717,575
Total liabilities and stockholders’ equity	$ 1,977,356	$ 2,150,172

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Preferred stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares designated (in shares)	0	0
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in usd per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	300,000,000	300,000,000
Common stock, shares issued (in shares)	176,505,000	173,530,000
Common stock, shares outstanding (in shares)	176,505,000	173,530,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Total revenue	$ 114,617	$ 1,193,323	$ 307,711
Operating costs and expenses:
Cost of goods sold	21,374	24,412	30,547
Research and development	434,566	399,536	268,461
General and administrative	98,712	81,443	52,364
Impairment of equipment and other costs for terminated program	0	0	15,981
Total operating costs and expenses	554,652	505,391	367,353
Income (loss) from operations	(440,035)	687,932	(59,642)
Non-operating income (expense):
Interest expense	(21,310)	(21,582)	(22,085)
Non-cash interest expense on liability related to sale of future royalties	(25,044)	(21,196)	(18,869)
Interest income and other income (expense), net	46,335	37,571	4,520
Total non-operating expense, net	(19)	(5,207)	(36,434)
Income (loss) before provision for income taxes	(440,054)	682,725	(96,076)
Provision for income taxes	613	1,412	616
Net income (loss)	$ (440,667)	$ 681,313	$ (96,692)
Net income (loss) per share
Basic ( in dollars per share)	$ (2.52)	$ 4.02	$ (0.62)
Diluted (in dollars per share)	$ (2.52)	$ 3.78	$ (0.62)
Weighted average shares outstanding used in computing net income (loss) per share
Basic (in shares)	174,993	169,600	155,953
Diluted (in shares)	174,993	180,119	155,953
Product sales
Revenue:
Total revenue	$ 20,117	$ 20,774	$ 32,688
Royalty revenue
Revenue:
Total revenue	41,222	41,976	33,527
Non-cash royalty revenue related to sale of future royalties
Revenue:
Total revenue	36,303	33,308	30,531
License, collaboration and other revenue
Revenue:
Total revenue	$ 16,975	$ 1,097,265	$ 210,965

Condensed Consolidated Statemen

Condensed Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ (440,667)	$ 681,313	$ (96,692)
Other comprehensive income (loss):
Net unrealized gain (loss) on available-for-sale investments	5,693	(2,975)	(533)
Net foreign currency translation gain (loss)	(382)	(1,230)	785
Other comprehensive income (loss)	5,311	(4,205)	252
Comprehensive income (loss)	$ (435,356)	$ 677,108	$ (96,440)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Shares	Capital in Excess of Par Value	Accumulated Other Comprehensive Income/(Loss)	Accumulated Deficit
Beginning Balance (in shares) at Dec. 31, 2016		153,212
Beginning Balance at Dec. 31, 2016	$ 88,125	$ 15	$ 2,111,483	$ (2,363)	$ (2,021,010)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)		6,312
Shares issued under equity compensation plans	59,528		59,528
Stock-based compensation	36,615		36,615
Other comprehensive income (loss)	252		239	252	(239)
Net income (loss) (1)	(96,692)				(96,692)
Ending Balance (in shares) at Dec. 31, 2017		159,524
Ending Balance at Dec. 31, 2017	$ 87,828	$ 15	2,207,865	(2,111)	(2,117,941)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Sale of stock to Bristol-Myers Squibb (Note 10) (in shares)	8,285
Sale of stock to Bristol-Myers Squibb (Note 10)	$ 790,232	$ 1	790,231
Shares issued under equity compensation plans (in shares)		5,721
Shares issued under equity compensation plans	61,729	$ 1	61,728
Stock-based compensation	88,101		88,101
Other comprehensive income (loss)	(4,205)			(4,205)
Net income (loss) (1)	681,313				681,313
Ending Balance (in shares) at Dec. 31, 2018		173,530
Ending Balance at Dec. 31, 2018	1,717,575	$ 17	3,147,925	(6,316)	(1,424,051)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Shares issued under equity compensation plans (in shares)		2,975
Shares issued under equity compensation plans	23,377	$ 0	23,377	0	0
Stock-based compensation	99,795		99,795	0	0
Other comprehensive income (loss)	5,311		0	5,311	0
Net income (loss) (1)	(440,667)		0	0	(440,667)
Ending Balance (in shares) at Dec. 31, 2019		176,505
Ending Balance at Dec. 31, 2019	$ 1,405,391	$ 17	$ 3,271,097	$ (1,005)	$ (1,864,718)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended			94 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Cash flows from operating activities:
Net income (loss)	$ (440,667,000)	$ 681,313,000	$ (96,692,000)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Non-cash royalty revenue related to sale of future royalties	(36,303,000)	(33,308,000)	(30,531,000)	$ (207,142,000)
Non-cash interest expense on liability related to sale of future royalties	25,044,000	21,196,000	18,869,000	166,693,000
Stock-based compensation	99,795,000	88,101,000	36,615,000
Depreciation and amortization	13,156,000	10,870,000	14,741,000
Impairment of equipment from terminated program	0	0	15,081,000
Accretion of discounts, net, and other non-cash transactions	(11,394,000)	(10,952,000)	(881,000)
Changes in operating assets and liabilities:
Accounts receivable	6,411,000	(25,505,000)	10,664,000
Inventory	(1,284,000)	(655,000)	383,000
Operating lease right-of-use assets, net of operating lease liabilities	13,090,000	0	0
Other assets	1,190,000	(31,652,000)	(4,800,000)
Accounts payable	12,967,000	971,000	2,074,000
Accrued compensation	1,530,000	1,674,000	(10,017,000)
Other accrued expenses	3,816,000	27,947,000	7,277,000
Deferred revenue	(16,565,000)	(15,331,000)	(28,269,000)
Other liabilities	533,000	3,545,000	(14,928,000)
Net cash provided by (used in) operating activities	(328,681,000)	718,214,000	(80,414,000)
Cash flows from investing activities:
Purchases of investments	(1,380,865,000)	(2,271,250,000)	(404,425,000)
Maturities of investments	1,614,036,000	890,957,000	347,743,000
Sales of investments	0	11,963,000	37,549,000
Purchases of property, plant and equipment	(26,285,000)	(14,239,000)	(9,676,000)
Sales of property and plant	0	2,633,000	0
Net cash provided by (used in) investing activities	206,886,000	(1,379,936,000)	(28,809,000)
Cash flows from financing activities:
Issuance of common stock to Bristol-Myers Squibb (Note 10)	0	790,231,000	0
Proceeds from shares issued under equity compensation plans	23,355,000	61,735,000	59,522,000
Payment of capital lease obligations	0	0	(5,131,000)
Net cash provided by financing activities	23,355,000	851,966,000	54,391,000
Effect of exchange rates on cash and cash equivalents	(102,000)	(101,000)	(46,000)
Net increase (decrease) in cash and cash equivalents	(98,542,000)	190,143,000	(54,878,000)
Cash and cash equivalents at beginning of year	194,905,000	4,762,000	59,640,000
Cash and cash equivalents at end of year	96,363,000	194,905,000	4,762,000	$ 96,363,000
Supplemental disclosure of cash flow information:
Cash paid for interest	19,199,000	19,471,000	20,116,000
Cash paid for income taxes	555,000	618,000	556,000
Right-of-use assets recognized in exchange for operating lease liabilities	$ 57,691,000	$ 0	$ 0

Organization and Summary of Sig

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Summary of Significant Accounting Policies	Organization and Summary of Significant Accounting Policies Organization We are a research-based biopharmaceutical company headquartered in San Francisco, California and incorporated in Delaware. We are developing a pipeline of drug candidates that utilize our advanced polymer conjugate technology platforms, which are designed to enable the development of new molecular entities that target known mechanisms of action. Our research and development pipeline of new investigational drugs includes treatments for cancer and autoimmune disease. 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, 2019 , we had approximately $1.6 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: Inheris Biopharma, Inc. (Inheris), Nektar Therapeutics (India) Private Limited and Nektar Therapeutics UK Limited. We have eliminated all intercompany accounts and transactions in consolidation. Our Consolidated Financial Statements are denominated in U.S. dollars. Accordingly, changes in exchange rates between the applicable foreign currency and the U.S. dollar will affect the translation of each foreign subsidiary’s financial results into U.S. dollars for purposes of reporting our consolidated financial results. We include translation gains and losses in accumulated other comprehensive loss in the stockholders’ equity section of our Consolidated Balance Sheets. To date, such cumulative currency translation adjustments have not been significant to our consolidated financial position. Our comprehensive income (loss) consists of our net income (loss) plus our foreign currency translation gains and losses and unrealized holding gains and losses on available-for-sale securities, neither of which were significant during the years ended December 31, 2019 , 2018 , and 2017 . In addition, there were no significant reclassifications out of accumulated other comprehensive loss to the statements of operations during the years ended December 31, 2019 , 2018 and 2017 . The preparation of consolidated financial statements in conformity with U.S. generally accepted accounting principles (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Accounting estimates and assumptions are inherently uncertain. Actual results could differ materially from those estimates and assumptions. Our estimates include those related to the selling prices of performance obligations and amounts of variable consideration in collaboration agreements, royalty revenue, and other assumptions required for revenue recognition as described further below; the net realizable value of inventory; the impairment of investments, goodwill and long-lived assets; contingencies, accrued clinical trial, contract manufacturing and other expenses; non-cash royalty revenue and non-cash interest expense from our liability related to our sale of future royalties; assumptions used in stock-based compensation; and ongoing litigation, among other estimates. We base our estimates on historical experience and on other assumptions that management believes are reasonable under the circumstances. These estimates form the basis for making judgments about the carrying values of assets and liabilities when these values are not readily apparent from other sources. As appropriate, we assess estimates each period, update them to reflect current information, and will generally reflect any changes in estimates in the period first identified. 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 coupon 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 primarily located in the U.S. and Europe and with whom we have multi-year arrangements. Our accounts receivable balance contains billed and unbilled trade receivables from product sales, milestones, other contingent payments and royalties, and cost-sharing billings from collaborative research and development agreements. For the year ended December 31, 2019 , our accounts receivable included $12.8 million under customer contracts from our collaboration partners and $24.0 million for unbilled net expense reimbursements from our collaboration partner Bristol-Myers Squibb Company (BMS). For the year ended December 31, 2018 , our accounts receivable included $24.2 million from customer contracts and $19.0 million for unbilled net expense reimbursements from BMS. We generally do not require collateral from our partners. We perform a regular review of our partners’ 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, 2019 , three partners represented 65% , 17% and 14% , respectively, of our accounts receivable. At December 31, 2018 , three different partners represented 44% , 36% and 12% , respectively, of our accounts receivable. Inventory and Significant Supplier Concentrations We generally manufacture inventory upon receipt of firm purchase orders from our collaboration partners, and we may manufacture certain intermediate work-in-process materials and purchase raw materials based on purchase forecasts from our collaboration partners. Inventory includes direct materials, direct labor, and manufacturing overhead, and we determine cost on a first-in, first-out basis for raw materials and on a specific identification basis for work-in-process and finished goods. We value inventory at the lower of cost or net realizable value, and we write down defective or excess inventory to net realizable value based on historical experience or projected usage. We expense inventory related to our research and development activities when we purchase or manufacture it. Before the regulatory approval of our drug candidates, we recognize research and development expense for the manufacture of drug products that could potentially be available to support the commercial launch of our drug candidates, if approved. We are dependent on our suppliers and contract manufacturers to provide raw materials and 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, if supplies are delayed or interrupted for any reason, our ability to develop and produce our drug candidates or our ability to meet our supply obligations could be significantly impaired, which could have a material adverse effect on our business, financial condition and results of operations. Leases On January 1, 2019, we adopted Accounting Standards Codification (ASC) 842, Leases (ASC 842). ASC 842 supersedes the guidance in ASC 840, Leases (ASC 840). Under ASC 842, an entity recognizes a right-of-use asset and a corresponding lease liability, measured as the present value of the lease payments. In our adoption, we used the package of practical expedients, which, among other things, allowed us to carry forward our historical lease classification of those leases in effect as of January 1, 2019. We present results for the year ended December 31, 2019 under ASC 842. We have not restated the results for the years ended December 31, 2018 and 2017 and our financial position as of December 31, 2018, and continue to report them under ASC 840. We determine if an arrangement contains a lease at the inception of the arrangement. Right-of-use assets represent our right to use an underlying asset for the lease term, and lease liabilities represent our obligation to make lease payments arising from the lease. We recognize operating lease right-of-use assets and liabilities at the lease commencement date based on the present value of lease payments over the expected lease term. In determining the present value of lease payments, we use our incremental borrowing rate based on the information available at the lease commencement date. However, in determining the present value of our lease payments for leases in effect when we adopted ASC 842, we used our incremental borrowing rate as of January 1, 2019. We elected the practical expedient to account for the lease and non-lease components, such as common area maintenance charges, as a single lease component for our facilities leases, and elected the short-term lease recognition exemption for our short-term leases, which allows us not to recognize lease liabilities and right-of-use assets for leases with an original term of twelve months or less. Our expected lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise any such options. We recognize lease expense for our operating leases on a straight-line basis over the expected lease term. We have elected to recognize lease incentives, such as tenant improvement allowances, at the lease commencement date as a reduction of the right-of-use asset and lease liability until paid to us by the lessor to the extent that the lease provides a specified fixed or maximum level of reimbursement and we are reasonably certain to incur reimbursable costs at least equaling such amounts. For leases in effect as of January 1, 2019, we recognized our lease incentives as part of our transition adjustment. As a result of our adoption of ASC 842, we recorded right-of-use assets of $ 83.5 million and lease liabilities of $ 96.2 million for our facilities operating leases, with no effect on our opening balance of accumulated deficit. Please see Note 6 for additional information regarding our leases. Long-Lived Assets We state property, plant and equipment at cost, net of accumulated depreciation. We capitalize major improvements and expense maintenance and repairs as incurred. We generally recognize depreciation on a straight-line basis. We depreciate manufacturing, laboratory and other equipment over their estimated useful lives of generally three to ten years , depreciate buildings over the estimated useful life of generally twenty years and amortize leasehold improvements over the shorter of the estimated useful lives or the remaining term of the related lease. Goodwill represents the excess of the price paid for another entity over the fair value of the assets acquired and liabilities assumed in a business combination. We are organized in one reporting unit and evaluate the goodwill for the Company as a whole. Goodwill has an indefinite useful life and is not amortized, but instead tested for impairment at least annually in the fourth quarter of each year using an October 1 measurement date. We assess the impairment of long-lived assets whenever events or changes in business circumstances indicate that the carrying amounts of the assets may not be fully recoverable. In the case of property, plant and equipment and right-of-use assets for our leases, we determine whether there has been an impairment by comparing the carrying value of the asset to the anticipated undiscounted net cash flows associated with the asset. If such cash flows are less than the carrying value, we write down the asset to its fair value, which may be measured as anticipated discounted net cash flows associated with the asset. In the case of goodwill impairment, we compare the carrying value of the reporting unit to its fair value, which we generally measure using market capitalization for our single reporting unit. If an impairment exists, we write down goodwill such that the carrying value of the reporting units equals its fair value. Collaborative Arrangements We enter into collaboration arrangements with pharmaceutical and biotechnology collaboration partners, under which we may grant licenses to our collaboration partners to further develop and commercialize one of our proprietary drug candidates, either alone or in combination with the collaboration partners’ compounds, or grant licenses to partners to use our technology to research and develop their own proprietary drug candidates. We may also perform research, development, manufacturing and supply activities under our collaboration agreements. Consideration under these contracts may include an upfront payment, development and regulatory milestones and other contingent payments, expense reimbursements, royalties based on net sales of approved drugs, and commercial sales milestone payments. Additionally, these contracts may provide options for the customer to purchase our proprietary PEGylation materials, drug candidates or additional contract research and development services under separate contracts. When we enter into collaboration agreements, we assess whether the arrangements fall within the scope of ASC 808, Collaborative Arrangements (ASC 808) based on whether the arrangements involve joint operating activities and whether both parties have active participation in the arrangement and are exposed to significant risks and rewards. To the extent that the arrangement falls within the scope of ASC 808, we assess whether the payments between us and our collaboration partner fall within the scope of other accounting literature. If we conclude that payments from the collaboration partner to us represent consideration from a customer, such as license fees and contract research and development activities, we account for those payments within the scope of ASC 606, Revenue from Contracts with Customers (ASC 606). However, if we conclude that our collaboration partner is not a customer for certain activities and associated payments, such as for certain collaborative research, development, manufacturing and commercial activities, we present such payments as a reduction of research and development expense or general and administrative expense, based on where we present the underlying expense. Additionally, if we reimburse our collaboration partners for these activities, we present such reimbursements as research and development expense or general and administrative expense, depending upon the nature of the underlying expense. Revenue Recognition For elements of those arrangements that we determine should be accounted for under ASC 606, we assess which activities in our collaboration agreements are performance obligations that should be accounted for separately and determine the transaction price of the arrangement, which includes the assessment of the probability of achievement of future milestones and other potential consideration. For arrangements that include multiple performance obligations, such as granting a license or performing contract research and development activities or participation on joint steering or other committees, we allocate upfront and milestone payments under a relative standalone selling price method. Accordingly, we develop assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. These key assumptions may include revenue forecasts, clinical development timelines and costs, discount rates and probabilities of clinical and regulatory success. Product sales Product sales are primarily derived from manufacturing and supply agreements with our customers. We have assessed our current manufacturing and supply arrangements and have generally determined that they provide the customer an option to purchase our proprietary PEGylation materials. Accordingly, we treat each purchase order as a discrete exercise of the customer’s option (i.e. a separate contract) rather than as a component of the overall arrangement. The pricing for the manufacturing and supply is generally at a fixed price and may be subject to annual producer price index (PPI) adjustments. We invoice and recognize product sales when title and risk of loss pass to the customer, which generally occurs upon shipment. Customer payments are generally due 30 days from receipt of invoice. We test our products for adherence to technical specifications 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 after 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 BMS, we record the cost reimbursement from our partner as a reduction to research and development expense when reimbursement amounts are due to us under the agreement. We record an accrued expense for the estimated costs of our clinical trial activities performed by third parties. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows to our vendors. Payments under the contracts depend on factors such as the achievement of certain events, successful enrollment of patients, and completion of certain clinical trial activities. We generally accrue costs associated with the start-up and reporting phases of the clinical trials ratably over the estimated duration of the start-up and reporting phases. We generally accrue costs associated with the treatment phase of clinical trials based on the estimated activities performed by our third parties. We may also accrue expenses based on the total estimated cost of the treatment phase on a per patient basis and expense the per patient cost ratably over the estimated patient treatment period based on patient enrollment in the trials. In specific circumstances, such as for certain time-based costs, we recognize clinical trial expenses using a methodology that we consider to be more reflective of the timing of costs incurred. We record an accrued expense for the estimated unbilled 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. We capitalize advance payments for goods or services that will be used or rendered for future research and development activities and recognize expense as the related goods are delivered or the services performed. We base our estimates on the best information available at the time. However, additional information may become available to us which may allow us to make a more accurate estimate in future periods. In this event, we may be required to record adjustments to research and development expenses in future periods when the actual level of activity becomes more certain. We consider such increases or decreases in cost as changes in estimates and reflect them 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, including but not limited to, our stock price volatility over the term of the awards, and actual and projected employee stock option exercise behaviors. Because our employee stock options have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models may not provide a reliable single measure of the fair value of our employee stock options or common stock purchased under the ESPP. The 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 grant date fair value 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. We recognize stock-based compensation expense for purchases under the ESPP over the respective six-month purchase period. We report expense amounts in cost of goods sold, research and development expense, and general and administrative expense based on the function of the applicable employee. Stock-based compensation charges are non-cash charges and have no effect on our reported cash flows. Net Income (Loss) Per Share For all periods presented in the Consolidated Statements of Operations, the net income (loss) available to common stockholders is equal to the reported net income (loss). We calculate basic net income (loss) per share based on the weighted-average number of common shares outstanding during the periods presented and calculate diluted net income (loss) per share based on the weighted-average number of shares of common stock outstanding, including potentially dilutive securities, which consist of common shares underlying stock options and restricted stock units (RSUs). For 2019 and 2017 , basic and diluted net loss per share are the same due to our net losses and the requirement to exclude potentially dilutive securities which would have an antidilutive effect on net loss per share. We excluded weighted average outstanding stock options and RSUs totaling 17.9 million and 20.6 million for 2019 and 2017 , respectively. 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. 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. Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12 - Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12). ASU 2019-12 created an exception to the incremental approach for intraperiod tax allocation when there is a loss from continuing operations and income or a gain from other items (for example, discontinued operations or other c

Cash and Investments in Marketa

Cash and Investments in Marketable Securities	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Cash and Investments in Marketable Securities	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, December 31, Cash and cash equivalents $ 96,363 $ 194,905 Short-term investments 1,228,499 1,140,445 Long-term investments 279,119 582,889 Total cash and investments in marketable securities $ 1,603,981 $ 1,918,239 We invest in liquid, high quality debt securities. Our investments in debt securities are subject to interest rate risk. To minimize the exposure due to an adverse shift in interest rates, we invest in securities with maturities of two years or less and maintain a weighted average maturity of one year or less. All of our long-term investments as of December 31, 2019 and 2018 had maturities between one and two years . Gross unrealized gains and losses were not significant at either December 31, 2019 or 2018 . During the year ended December 31, 2019 , we sold no available-for-sale securities and during the years ended December 31, 2018 and 2017 , we sold available-for-sale securities totaling $12.0 million and $37.5 million , respectively, and realized gains and losses were not significant in any of those periods. Our portfolio of cash and investments in marketable securities includes (in thousands): Fair Value Hierarchy Level Estimated Fair Value at December 31, December 31, Corporate notes and bonds 2 $ 1,132,182 $ 1,288,986 Corporate commercial paper 2 375,473 498,048 Obligations of U.S. government agencies 2 — 12,977 Available-for-sale investments 1,507,655 1,800,011 Money market funds 1 83,546 105,656 Certificate of deposit N/A 6,951 6,760 Cash N/A 5,829 5,812 Total cash and investments in marketable securities $ 1,603,981 $ 1,918,239 _______________________________________________________________ Level 1 — Quoted prices in active markets for identical assets or liabilities. Level 2 — Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices for identical or similar assets or liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. We use a market approach to value our Level 2 investments. The disclosed fair value related to our investments is based on market prices from a variety of industry standard data providers and generally represents quoted prices for similar assets in active markets or has been derived from observable market data. For the years ended December 31, 2019 and 2018, there were no transfers between Level 1 and Level 2 of the fair value hierarchy. Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. At December 31, 2019 and 2018 , we had letter of credit arrangements in favor of our landlords and certain vendors totaling $6.8 million and $6.6 million , respectively. These letters of credit are secured by investments of similar amounts.

Inventory

Inventory	12 Months Ended
	Dec. 31, 2019
Inventory Disclosure [Abstract]
Inventory	Inventory Inventory consists of the following (in thousands): December 31, 2019 2018 Raw materials $ 1,673 $ 1,846 Work-in-process 8,267 6,403 Finished goods 2,725 3,132 Total inventory $ 12,665 $ 11,381

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, Plant and Equipment Property, plant and equipment consists of the following (in thousands): December 31, 2019 2018 Building and leasehold improvements $ 93,097 $ 77,771 Laboratory equipment 36,623 33,806 Computer equipment and software 26,910 23,395 Manufacturing equipment 22,030 21,339 Furniture, fixtures, and other 9,662 7,959 Depreciable property, plant and equipment at cost 188,322 164,270 Less: accumulated depreciation (127,875 ) (120,507 ) Depreciable property, plant and equipment, net 60,447 43,763 Construction-in-progress 4,552 5,088 Property, plant and equipment, net $ 64,999 $ 48,851 Building and leasehold improvements include our manufacturing, research and development and administrative facilities and the related improvements to these facilities. Our leasehold improvements increased significantly during the year ended December 31, 2019 due to the construction of leasehold improvements for our new facilities on Third Street as further described in Note 6. 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, 2019 , 2018 , and 2017 was $11.0 million , $8.8 million , and $12.6 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 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

Senior Secured Notes	12 Months Ended
	Dec. 31, 2019
Debt Disclosure [Abstract]
Senior Secured Notes	Senior Secured Notes On October 5, 2015, we completed the sale and issuance of $250.0 million in aggregate principal amount of 7.75% senior secured notes due 2020 (the Notes). The Notes are secured by a first-priority lien on substantially all of our assets (except our right-of-use 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 days 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 recorded as a discount to the senior secured notes, net liability balance in our Consolidated Balance Sheet. The unamortized balance of these costs totals $1.3 million at December 31, 2019 , which we will amortize 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 100% of the principal amount of the Notes plus 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, 2019 , 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 $252.6 million .

Leases

Leases	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Leases	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, effectively extending our lease term from 2020 to 2030 for our 148,263 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, which we have excluded from our determination of the lease term. The monthly base rent for the Mission Bay Facility will escalate over the term of the lease at various intervals. During the term of the Mission Bay Lease, we are responsible for paying our share of operating expenses specified in the lease, including utilities, common area maintenance, insurance costs and taxes. During the year ended December 31, 2019 , ARE delivered 13,907 square feet of space, and therefore we recognized right-of-use assets and lease liabilities of $6.7 million for the space. The Mission Bay Lease also obligates us to rent from ARE a total of an additional approximately 4,940 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. (Kilroy) to lease 135,936 square feet of space located at 360 Third Street, San Francisco, California (the Third Street Facility) from June 2018 to January 31, 2030 , subject to our right to extend the term for a consecutive five-year period, which we have excluded from our determination of the lease term. Kilroy delivered an initial 1,726 square feet in June 2018, a total of 67,105 square feet in December 2018, and the final 67,105 square feet in August 2019. As a result of the delivery of the final spaces during the year ended December 31, 2019, we recognized an additional right-of-use asset and lease liability of $51.0 million . The Third Street Lease provides us additional facilities to support our San Francisco-based R&D activities. Our fixed 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 one-time right of first offer with respect to certain additional rental space at the Third Street Facility. The Third Street Lease includes various covenants, indemnities, defaults, termination rights, security deposits and other provisions customary for lease transactions of this nature. We recognize rent expense for these operating leases on a straight-line basis over the lease period. The components of lease costs, which we include in operating expenses in our Condensed Consolidated Statements of Operations, were as follows (in thousands): Year Ended December 31, 2019 2018 2017 Operating lease cost $ 14,697 $ 7,972 $ 4,515 Variable lease cost 6,408 4,497 3,077 Total lease costs $ 21,105 $ 12,469 $ 7,592 During the year ended December 31, 2019 , we recorded operating lease expense of $14.7 million and paid $8.4 million of operating lease payments related to our lease liabilities, which we include in net cash provided by (used in) operating activities in our Consolidated Statement of Cash Flows. As of December 31, 2019 , the maturities of our operating lease liabilities were as follows (in thousands): Year ending December 31, 2020 $ 14,571 2021 19,219 2022 19,832 2023 20,461 2024 21,110 2025 and thereafter 118,058 Total lease payments 213,251 Less: portion representing interest (54,741 ) Less: lease incentives (3,264 ) Operating lease liabilities 155,246 Less: current portion (12,516 ) Operating lease liabilities, less current portion $ 142,730 As of December 31, 2019 , the weighted-average remaining lease term is 10.1 years and the weighted-average discount rate used to determine the operating lease liability was 5.9% . Under the historical guidance of ASC 840, our deferred rent balance at December 31, 2018 totaled $9.3 million and our future minimum lease payments for our operating leases at December 31, 2018 were 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 o

Liability Related to the Sale of Future Royalties	12 Months Ended
	Dec. 31, 2019
Liability Related To Sale Of Potential Future Royalties [Abstract]
Liability Related to Sale of Future Royalties	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 we will amortize 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 as royalties from the CIMZIA ® and MIRCERA ® products are remitted directly to RPI. The following table shows the activity within the liability account during the year ended December 31, 2019 and for the period from the inception of the royalty transaction on February 24, 2012 (inception) to December 31, 2019 (in thousands): Year ended Period from Liability related to the sale of future royalties—beginning balance $ 84,810 $ — Proceeds from sale of future royalties — 124,000 Payments from Nektar to RPI — (10,000 ) Non-cash CIMZIA ® and MIRCERA ® royalty revenue (36,303 ) (207,142 ) Non-cash interest expense recognized 25,044 166,693 Liability related to the sale of future royalties – ending balance 73,551 73,551 Less: unamortized transaction costs (1,531 ) (1,531 ) Liability related to the sale of future royalties, net $ 72,020 $ 72,020 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, 2019 , 2018 and 2017 , we recognized $36.3 million , $33.3 million , and $30.5 million , respectively, in non-cash royalties from net sales of CIMZIA ® and MIRCERA ® , and we recorded $25.0 million , $21.2 million and $18.9 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. 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, net of our payments to RPI, will be recorded as interest expense over the life of the Royalty Obligation. 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. From inception through 2017, our estimate of the total interest expense on the Royalty Obligation resulted in an effective annual interest rate of approximately 17% . During the three months ended December 31, 2017, our estimate of the effective annual interest rate over the life of the agreement increased to 17.6% , which resulted in a prospective interest rate of 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 resulted in a prospective interest rate of 29% . During the three month period ended December 31, 2019, primarily as a result of increases in the forecasted sales of CIMZIA ® and MIRCERA ® , our estimate of the effective annual interest rate over the life of the agreement increased to 19.5% , which results in a prospective interest rate of 38% . 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

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Purchase Commitments In the normal course of business, we enter into various firm purchase commitments related to contract manufacturing, clinical development and certain other items. As of December 31, 2019 , these commitments were approximately $25.8 million , all of which we expect to pay in 2020. Legal Matters From time to time, we are involved in lawsuits, audits, arbitrations, claims, investigations and proceedings, consisting of intellectual property, commercial, employment, regulatory, and other matters, which arise in the ordinary course of business. We make provisions for liabilities when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. Such provisions are reviewed at least quarterly and adjusted to reflect the impact of settlement negotiations, judicial and administrative rulings, advice of legal counsel, and other information and events pertaining to a particular case. Litigation is inherently unpredictable. If any unfavorable ruling were to occur in any specific period, there exists the possibility of a material adverse impact on the results of our operations of that period and on our cash flows and liquidity. On October 30, 2018, we and certain of our executives were named in a putative securities class action complaint filed in the U.S. District Court for the Northern District of California, which complaint was subsequently amended on May 15, 2019. Also, on February 13, 2019, and February 18, 2019, shareholder derivative complaints were filed in the U.S. District Court for the District of Delaware naming the CEO, CFO and certain members of Nektar’s board. These class action and shareholder derivative actions assert, among other things, that for a period beginning at least from November 11, 2017 through October 2, 2018, our stock was inflated due to alleged misrepresentations about the efficacy and safety of bempegaldesleukin. In addition, on August 19, 2019, we and certain of our executives were named in a putative securities class action complaint filed in the U.S. District Court for the Northern District of California, which complaint was subsequently amended on January 24, 2020. Also, on February 11, 2020, and on February 20, 2020, shareholder derivative complaints were filed in the U.S. District Court for the Northern District of California naming the CEO, CFO and certain members of Nektar's board. These class action and shareholder derivative actions assert, among other things, that for a period between February 15, 2019 and August 8, 2019, inclusive, our stock was inflated due to an alleged failure to disclose a reduction in the planned number of bempegaldesleukin clinical trials and a bempegaldesleukin manufacturing issue. All of these cases are in the early stages. Accordingly, we cannot reasonably estimate a potential future loss or a range of potential future losses, and we have not recorded any accrual for a contingent liability associated with these legal proceedings. However, an unfavorable resolution could potentially have a material adverse effect on our business, financial condition, and results of operations or prospects, and potentially result in paying monetary damages. We have recorded no liability for these matters on our Consolidated Balance Sheets as of December 31, 2019 or 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, 2019 or 2018 . Indemnifications in Connection with Commercial Agreements As part of our collaboration agreements with our partners related to the license, development, manufacture and supply of drugs and PEGylation materials based on our proprietary technologies and drug candidates, we generally agree to defend, indemnify and hold harmless our partners from and against third party liabilities arising out of the agreement, including product liability (with respect to our activities) and infringement of intellectual property to the extent the intellectual property is developed by us and licensed to our partners. The term of these indemnification obligations is generally perpetual any time after execution of the agreement. There is generally no limitation on potential amount of future payments we could be required to make under these indemnification obligations. From time to time, we enter into other strategic agreements such as divestitures and financing transactions pursuant to which we are required to make representations and warranties and undertake to perform or comply with certain covenants, including our obligation to RPI described in Note 7. In the event it is determined that we breached certain of the representations and warranties or covenants made by us in any such agreements, 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 $5.0 million per incident for merger and acquisition related claims, $5.0 million per incident for securities related claims and $1.5 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

Stockholders' Equity	12 Months Ended
	Dec. 31, 2019
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Common Stock As discussed in Note 10, on April 3, 2018, we completed the issuance and sale of 8,284,600 shares of our common stock under a Share Purchase Agreement with BMS. These shares are unregistered and subject to certain lock-up and stand-still provisions for a five -year period. Equity Compensation Plans At December 31, 2019 , we had 28,962,018 reserved shares of common stock, all of which are reserved for issuance under our equity compensation plans, of which approximately 19,817,000 shares may be issued upon the exercise of outstanding options or the vesting of restricted stock units (RSUs) and 9,145,000 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 option granted under the 2017 Plan, as well as any shares exchanged or withheld to satisfy the tax withholding obligations related to any award, will not be available for subsequent awards under the 2017 Plan. The purpose of the 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 2018 and 2019 . 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, amended on June 16, 2015 by approval of our stockholders to make available for award grants 7,000,000 additional shares, 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; (iii) the 2000 Equity Incentive Plan (2000 Plan) which was adopted by the Board of Directors on April 19, 2000 by amending and restating our 1994 Equity Incentive Plan, and which expired on February 9, 2010; and (iv) 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, the 2008 Plan and the 2000 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. Pursuant to the 2000 Non-Officer Plan, we previously granted or issued non-qualified stock options, rights to acquire restricted stock and stock bonuses to employees and consultants who are neither officers nor directors of Nektar. 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, 2019 , 2018 , and 2017 , we recognized $3.5 million , $2.8 million , and $1.6 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 following a change of control transaction, all other employees would each be entitled to receive cash severance pay equal to 6 months base salary plus a pro-rata portion of annual target incentive pay, the extension of employee benefits over this severance period and the full acceleration of each such employee’s unvested outstanding equity awards. Under the CIC Plan, as amended, non-employee directors would also be entitled to full acceleration of vesting of all outstanding stock awards in the event of a change of control transaction.

License and Collaboration Agree

License and Collaboration Agreements	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License and Collaboration Agreements	License and Collaboration Agreements We have entered into various collaboration agreements including license agreements and collaborative research, development and commercialization agreements with various pharmaceutical and biotechnology companies. Under these collaboration arrangements, we are entitled to receive license fees, upfront payments, milestone and other contingent payments, royalties, sales milestone payments, and payments for the manufacture and supply of our proprietary PEGylation materials and/or reimbursement for research and development activities. Our partners may generally cancel our collaboration agreements without significant financial penalty. We generally include our costs of performing these services in research and development expense, except for costs for product sales to our collaboration partners which we include in cost of goods sold. We analyze our agreements to determine whether we should account for the agreements within the scope of ASC 808, 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. In accordance with our collaboration agreements, we recognized license, collaboration and other revenue as follows (in thousands): Year Ended December 31, Partner Agreement 2019 2018 2017 Bristol-Myers Squibb NKTR-214 $ — $ 1,059,768 $ — Eli Lilly and Company NKTR-358 7,019 11,634 130,087 Amgen, Inc. Neulasta ® 5,000 5,000 5,000 Baxalta Incorporated / Takeda Hemophilia, including ADYNOVATE ® and ADYNOVI™ 378 20,328 11,443 Ophthotech Corporation(1) Fovista ® — — 19,123 Bayer Healthcare LLC(1) BAY41-6551 (Amikacin Inhale) — — 17,931 AstraZeneca AB MOVANTIK ® and MOVENTIG ® — — 4,600 Other 4,578 535 22,781 License, collaboration and other revenue $ 16,975 $ 1,097,265 $ 210,965 _______________________________________________________________ (1) These collaboration agreements were completed as of December 31, 2017. For the years ended December 31, 2019 and 2018 , we recognized $77.5 million and $95.3 million of revenue for performance obligations that we had satisfied in prior periods, respectively. For both years, this amount includes all of our royalty revenue and non-cash royalty revenue because these royalties substantially relate to the licenses that we had previously granted. For the year ended December 31, 2018, this amount also included the $10.0 million ADYNOVATE ® sales milestone and the $10.0 million development milestone from Baxalta described below. The following table presents the changes in our deferred revenue balance from our collaboration agreements during the year ended December 31, 2019 (in thousands): For the year ended Deferred revenue—December 31, 2018 $ 24,636 Recognition of previously unearned revenue (16,565 ) Deferred revenue—December 31, 2019 $ 8,071 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 $5.5 million of our deferred revenue over the next twelve months. As of December 31, 2019 , 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. There have been no material changes to our collaboration agreements for the year ended December 31, 2019 , except as described below. Bristol-Myers Squibb (BMS): Bempegaldesleukin (previously referred to as NKTR-214) On February 13, 2018, we entered into a Strategic Collaboration Agreement (BMS Collaboration Agreement) and a Share Purchase Agreement with BMS, both of which became effective on April 3, 2018. Pursuant to these agreements, we and BMS are jointly developing bempegaldesleukin, including, without limitation, in combination with BMS’s Opdivo ® and Opdivo ® plus Yervoy ® (ipilimumab), and other compounds of BMS, us or any third party. The parties have agreed to jointly commercialize bempegaldesleukin on a worldwide basis. We retained the right to record all worldwide sales for bempegaldesleukin. We will share global commercialization profits and losses with BMS for bempegaldesleukin, with Nektar sharing 65% and BMS sharing 35% of the net profits and losses. The parties will share the internal and external development costs for bempegaldesleukin in combination regimens based on each party’s relative ownership interest in the compounds included in the regimens. In accordance with the agreement, the parties will share development costs for bempegaldesleukin in combination with Opdivo ® , 67.5% of costs to BMS and 32.5% to Nektar, and for bempegaldesleukin in a triplet combination with Opdivo ® and Yervoy ® , 78% of costs to BMS and 22% to Nektar. The parties will share costs for the manufacturing of bempegaldesleukin, 35% of costs to BMS and 65% to Nektar. The BMS Collaboration Agreement superseded and replaced the Clinical Trial Agreement we entered into with BMS in September 2016 to develop bempegaldesleukin in combination with Opdivo ® . Under the Clinical Trial Agreement, we acted as the sponsor of each Combination Therapy Trial and BMS was responsible for 50% of all out-of-pocket costs reasonably incurred in connection with third party contract research organizations, laboratories, clinical sites and institutional review boards. We recorded cost reimbursement payments to us from BMS as a reduction to research and development expense. Each party was otherwise responsible for its own internal costs, including internal personnel costs, incurred in connection with each Combination Therapy Trial. Upon the effective date of the BMS Collaboration Agreement in April 2018, BMS paid us a non-refundable upfront cash payment of $1.0 billion . We are eligible to receive additional cash payments up to a total of approximately $1.4 billion upon the achievement of certain development and regulatory milestones and up to a total of $350.0 million upon the achievement of certain sales milestones. In April 2018, BMS also purchased 8,284,600 shares of our common stock pursuant to the Share Purchase Agreement for total additional cash consideration of $850.0 million . On January 9, 2020, we and BMS entered into Amendment No. 1 (the Amendment) to the BMS Collaboration Agreement. Pursuant to the Amendment, we and BMS agreed to update the Collaboration Development Plan under which we are collaborating and developing bempegaldesleukin. The cost sharing under the Amendment remains unchanged. Additionally, we are eligible to receive an additional non-refundable, non-creditable milestone payment of $25.0 million following the achievement of the first patient, first visit in the registrational adjuvant melanoma trial, studying the combination of bempegaldesleukin and Opdivo ® . We are also eligible to receive non-refundable, creditable milestone payments of $25.0 million and $75.0 million following the achievement of the first patient, first visit in a registrational muscle-invasive bladder cancer trial and a registrational first-line non-small-cell lung cancer trial, respectively, in each case studying the combination of bempegaldesleukin and Opdivo ® . For the two creditable milestones, BMS is entitled to deduct the amounts paid pursuant to these milestones from future development milestones due to us under the original agreement. In January 2020, the milestone for the first patient, first visit milestone for the registrational muscle-invasive bladder cancer trial was achieved. BMS has the right, at its sole discretion, to terminate co-funding its share of the development costs for the adjuvant melanoma collaboration study if the metastatic melanoma collaboration study fails to meet the primary endpoint of progression free survival. If BMS exercises such right, we have the right, in our sole discretion, to continue the adjuvant melanoma study. We determined that the BMS Collaboration Agreement falls within the scope of ASC 808. As mentioned above, BMS shares certain percentages of development costs incurred by us and we share certain percentages of development costs incurred by BMS. We consider these activities to represent collaborative activities under ASC 808 and we recognize such cost sharing proportionately with the performance of the underlying services. We recognize BMS’ reimbursement of our expenses as a reduction of research and development expense and our reimbursement of BMS’ expenses as research and development expense. For the years ended December 31, 2019 , 2018 and 2017, we recorded $105.4 million and $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, 2019 and 2018, we have recorded an unbilled receivable of $24.0 million and $ 19.0 million, respectively, 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 bempegaldesleukin 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 and December 31, 2019 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. We updated the arrangement transaction price for this milestone upon achievement 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. 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, which we report in license, collaboration and other revenue . 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. We have an unsatisfied performance obligation related to our ongoing supply of PEGylation materials at a price less than their standalone selling prices. As of December 31, 2019 , our deferred revenue related to this agreement is not significant. Eli Lilly and Company (Lilly): NKTR-358 On July 23, 2017, we entered into a worldwide license agreement with Eli Lilly and Company (Lilly), which became effective on August 23, 2017, to co-develop NKTR-358, a novel immunological drug candidate that we invented. Under the terms of the agreement, we (i) received an initial payment of $150.0 million in September 2017 and are eligible for up to $250.0 million in additional development milestones, (ii) will co-develop NKTR-358 with Lilly for which we are responsible for completing Phase 1 clinical development and certain drug product development and supply activities, (iii) will share with Lilly Phase 2 development costs with 75% of those costs borne by Lilly and 25% of the costs borne by 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 and have not updated the transaction prices for any milestones as of December 31, 2019 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 as our conclusions remain unchanged. 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, 2019 , we have deferred revenue of approximately $1.3 million related to this agreement, which we expect to recognize through early 2020. 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, 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, 2019 , we have deferred revenue of approximately $4.2 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 Fovista ® in certain combination therapies 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 using our proprietary nebulizer devices. 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, 2019 , we have received a total of $385.0 million of upfront and contingent milestone payments from this agreement, all of which was received in or before 2015. 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 year ended December 31, 2017 , we recognized a total of $4.6 million related to our share of license-related payments made from Kirin to AstraZeneca. As of December 31, 2019 , we do not have deferred revenue related to our agreement with AstraZeneca. Other In addition, as of December 31, 2019 , we have a number of other collaboration agreements, including with our collaboration partner UCB Pharma, under which we are entitled to up to a total of $40.0 million of development milestone payments upon achievement of certain development objectives, as well as sales milestones upon achievement of annual sales targets and royalties based on net sales of commercialized products, if any. However, given the current phase of development of the potential products under these collaboration agreements, we cannot estimate the probability or timing of achieving these milestones and, therefore, have excluded all development milestones from the respective transaction prices for these agreements. In the three months ended December 31, 2019, one of our collaboration partners terminated the collaboration agreement with us, and we recognized $4.0 million of deferred revenue resulting from this arrangement. As of December 31, 2019 , we have deferred revenue of approximately $2.0 million related to these other collaboration agreements.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation	Stock-Based Compensation We recognize total stock-based compensation expense in our Condensed Consolidated Statements of Operations as follows (in thousands): Year Ended December 31, 2019 2018 2017 Cost of goods sold $ 4,294 $ 4,629 $ 2,333 Research and development 63,224 56,193 21,252 General and administrative 32,277 27,279 13,030 Total stock-based compensation $ 99,795 $ 88,101 $ 36,615 As of December 31, 2019 , total unrecognized compensation costs of $213.7 million related to unvested stock-based compensation arrangements are expected to be recognized as expense over a weighted-average period of 1.75 years. Stock-based compensation expense resulting from our ESPP was not significant in the years ended December 31, 2019 , 2018 , and 2017 . Black-Scholes Assumptions The following table lists the Black-Scholes option-pricing model assumptions used to calculate the fair value of employee and director stock options, as well as the resulting grant-date fair value: Year Ended December 31, 2019 2018 2017 Average risk-free interest rate 1.8 % 2.8 % 2.0 % Dividend yield 0.0 % 0.0 % 0.0 % Average volatility factor 62.2 % 61.0 % 54.2 % Weighted-average expected life 5.6 years 5.1 years 5.3 years Weighted-average grant-date fair value of options granted $ 12.25 $ 29.86 $ 20.08 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, 2018 15,930 $ 26.18 Options granted 1,842 21.86 Options exercised (1,629 ) 11.68 Options forfeited & canceled (1,258 ) 49.91 Outstanding at December 31, 2019 14,885 $ 25.23 4.31 $ 73,134 Exercisable at December 31, 2019 9,938 20.79 3.14 $ 66,707 _______________________________________________________________ (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, 2019 . The intrinsic value of options exercised during the years ended December 31, 2019, 2018 and 2017 totaled $30.6 million , $303.4 million and $84.0 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, 2018 3,320 $ 41.57 Granted 3,189 23.32 Vested and released (1,159 ) 36.33 Forfeited and canceled (415 ) 43.19 Balance at December 31, 2019 4,935 $ 30.85 $ 106,506 The fair value of restricted stock that vested in the years ended December 31, 2019 , 2018 and 2017 totaled $32.4 million , $80.4 million and $22.3 million , respectively.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income (loss) before provision for income taxes includes the following components (in thousands): Year Ended December 31, 2019 2018 2017 Domestic $ (441,494 ) $ 680,423 $ (97,938 ) Foreign 1,440 2,302 1,862 Income (loss) before provision for income taxes $ (440,054 ) $ 682,725 $ (96,076 ) Provision for Income Taxes The provision for income taxes consists of the following (in thousands): Year Ended December 31, 2019 2018 2017 Current: Federal $ — $ — $ — State 139 699 1 Foreign 495 620 580 Total Current 634 1,319 581 Deferred: Federal — — — State — — — Foreign (21 ) 93 35 Total Deferred (21 ) 93 35 Provision for income taxes $ 613 $ 1,412 $ 616 Income tax provision related to continuing operations differs from the amount computed by applying the statutory income tax rate of 21% for the years ended December 31, 2019 and 2018 and 35% for the year ended December 31, 2017 to pretax income (loss) as follows (in thousands): Year Ended December 31, 2019 2018 2017 Income tax expense (benefit) at federal statutory rate $ (92,411 ) $ 143,372 $ (33,627 ) Research credits (10,511 ) (17,295 ) (8,038 ) Sale of future royalties (7,624 ) (6,995 ) (8,236 ) Stock-based compensation (672 ) (66,716 ) (20,665 ) Premium on equity issuance — (12,551 ) — Change in valuation allowance 104,440 (46,885 ) (186,124 ) Non-cash interest expense on liability related to sale of future royalties 5,259 4,451 6,604 Non-deductible officers’ compensation 737 3,182 2,547 Tax law changes 23 45 248,155 Other 1,372 804 — Provision for income taxes $ 613 $ 1,412 $ 616 Tax Law Changes The U.S. Tax Cuts and Jobs Act (the TCJA) was enacted on December 22, 2017. The TCJA reduced the U.S. federal corporate tax rate from 35% in 2017 to 21% in 2018 , required companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and created new taxes on certain foreign sourced earnings. At December 31, 2018, we completed our accounting for the tax effects of the TCJA, which, other than the decrease in the valuation of our federal deferred tax assets discussed below, 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. Significant components of our deferred tax assets for federal and state income taxes are as follows (in thousands): December 31, 2019 2018 Deferred tax assets: Net operating loss carryforwards $ 399,361 $ 300,693 Research and other credits 128,015 116,955 Operating lease liabilities 36,907 — Stock-based compensation 30,875 21,518 Property, plant and equipment 5,021 2,124 Capitalized research expenses 3,705 8,072 Reserves and accruals 2,934 8,066 Deferred revenue 1,908 4,467 Deferred tax assets before valuation allowance 608,726 461,895 Valuation allowance for deferred tax assets (575,087 ) (460,455 ) Total deferred tax assets 33,639 1,440 Operating lease right-of-use assets (31,718 ) — Other (1,725 ) (1,270 ) Total deferred tax liabilities (33,443 ) (1,270 ) Net deferred tax assets $ 196 $ 170 Realization of our deferred tax assets is dependent upon future earnings, if any, the timing and amount of which are uncertain. Because of our lack of U.S. earnings history, other than income resulting from revenue recognized from the BMS Collaboration Agreement, and projected future losses, we have fully reserved our net U.S. deferred tax assets with a valuation allowance. The valuation allowance increased by $114.6 million during the year ended December 31, 2019 due to our net loss and decreased by $35.7 million and $169.3 million during the years ended December 31, 2018 and 2017, respectively. 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 primarily reflects the change in the federal rate. The valuation allowance includes approximately $35.6 million of income tax benefit at both December 31, 2019 and December 31, 2018 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 TCJA 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 did not record 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, 2019 , we had a net operating loss carryforward for federal income tax purposes of approximately $1,721.7 million , portions of which will begin to expire in 2022 . As of December 31, 2019 , we had a total state net operating loss carryforward of approximately $1,221.3 million , portions of which will begin to expire in 2026 . Utilization of some of the federal and state net operating loss and credit carryforwards are subject to annual limitations due to the “change in ownership” provisions of the Internal Revenue Code of 1986 and similar state provisions. We have federal research credits of approximately $94.8 million , which will begin to expire in 2020 and state research credits of approximately $49.4 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, 2017 and 2018 . We have the following activity relating to unrecognized tax benefits (in thousands): December 31, 2019 2018 2017 Beginning balance $ 27,419 $ 20,483 $ 18,413 Tax positions related to current year Additions: Federal 1,365 2,019 1,206 State 48,493 3,645 1,666 Reductions — — — Tax positions related to prior year Additions: Federal — 669 — State 277 603 — Foreign — — — Reductions (144 ) — (802 ) Settlements — — — Lapses in statute of limitations — — — Ending balance $ 77,410 $ 27,419 $ 20,483 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, 2019 , 2018 and 2017 , no significant interest or penalties were recognized relating to unrecognized tax benefits.

Segment Reporting

Segment Reporting	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Segment Reporting	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 UCB Pharma, Takeda, and AstraZeneca represented 28% , 19% and 17% of our revenue, respectively, for the year ended December 31, 2019 . Revenue from BMS represented 89% of our revenue, for the year ended December 31, 2018. Revenue from Lilly and UCB Pharma represented 42% and 12% of our revenue, respectively, for the year ended December 31, 2017 . 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, 2019 2018 2017 United States $ 27,093 $ 1,090,794 $ 190,810 Rest of World 87,524 102,529 116,901 Total revenue $ 114,617 $ 1,193,323 $ 307,711 At December 31, 2019 , $59.7 million , or approximately 92% , of the net book value of our property, plant and equipment was located in the United States and $5.3 million , or approximately 8% , was located in India. 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.

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2019
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event On January 14, 2020, the FDA held an Advisory Committee meeting regarding our NDA for NKTR-181. The Advisory Committee voted against approval. We subsequently decided to withdraw our NDA and to make no further investments in this program. On February 26, 2020, the Audit Committee of our Board of Directors approved management’s plan for the wind-down of Inheris and the NKTR-181 program. As a result, in the first quarter of 2020, we expect to incur charges of $45.0 million to $50.0 million , including non-cash charges of $19.7 million for the impairment of advance payments to contract manufacturers for commercial batches of NKTR-181, as well as other charges, primarily for non-cancellable commitments to our contract manufacturers and certain severance costs.

Selected Quarterly Financial Da

Selected Quarterly Financial Data	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Data	Selected Quarterly Financial Data (Unaudited) The following table sets forth certain unaudited quarterly financial data. In our opinion, the unaudited information set forth below has been prepared on the same basis as our audited information and includes all adjustments necessary to present fairly the information set forth herein. We have experienced fluctuations in our quarterly results and expect these fluctuations to continue in the future. Due to these and other factors, we believe that quarter-to-quarter comparisons of our operating results will not be meaningful, and the results for any one quarter may not be indicative of our future performance. 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, 2019 Year Ended December 31, 2018 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Product sales $ 4,398 $ 4,346 $ 5,558 $ 5,815 $ 6,295 $ 5,863 $ 4,256 $ 4,360 Total revenue $ 28,222 $ 23,315 $ 29,218 $ 33,862 $ 38,018 $ 1,087,717 $ 27,762 $ 39,826 Cost of goods sold $ 5,440 $ 5,018 $ 4,927 $ 5,989 $ 6,646 $ 5,522 $ 4,783 $ 7,461 Research and development expenses $ 118,463 $ 106,686 $ 99,048 $ 110,369 $ 99,424 $ 88,334 $ 102,895 $ 108,883 Operating income (loss) $ (120,687 ) $ (110,970 ) $ (98,740 ) $ (109,638 ) $ (86,739 ) $ 973,600 $ (98,634 ) $ (100,295 ) Net income (loss) (1) $ (119,632 ) $ (110,286 ) $ (98,585 ) $ (112,164 ) $ (95,792 ) $ 971,460 $ (96,143 ) $ (98,212 ) Net income (loss) per share(1) (2) Basic $ (0.69 ) $ (0.63 ) $ (0.56 ) $ (0.64 ) $ (0.60 ) $ 5.67 $ (0.56 ) $ (0.57 ) Diluted $ (0.69 ) $ (0.63 ) $ (0.56 ) $ (0.64 ) $ (0.60 ) $ 5.33 $ (0.56 ) $ (0.57 ) _______________________________________________________________ (1) As discussed in Note 1, in the fourth quarter of 2019, we adopted ASU 2019-12, effective January 1, 2019, which affected previously reported amounts of net loss and net loss per share for the first three quarters of 2019. We have recast such amounts for the effects of adoption. (2) 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 S_2

Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization We are a research-based biopharmaceutical company headquartered in San Francisco, California and incorporated in Delaware. We are developing a pipeline of drug candidates that utilize our advanced polymer conjugate technology platforms, which are designed to enable the development of new molecular entities that target known mechanisms of action. Our research and development pipeline of new investigational drugs includes treatments for cancer and autoimmune disease.
Basis of Presentation, Principles of Consolidation and Use of Estimates	Basis of Presentation, Principles of Consolidation and Use of Estimates Our Consolidated Financial Statements include the financial position, results of operations and cash flows of our wholly-owned subsidiaries: Inheris Biopharma, Inc. (Inheris), Nektar Therapeutics (India) Private Limited and Nektar Therapeutics UK Limited. We have eliminated all intercompany accounts and transactions in consolidation. Our Consolidated Financial Statements are denominated in U.S. dollars. Accordingly, changes in exchange rates between the applicable foreign currency and the U.S. dollar will affect the translation of each foreign subsidiary’s financial results into U.S. dollars for purposes of reporting our consolidated financial results. We include translation gains and losses in accumulated other comprehensive loss in the stockholders’ equity section of our Consolidated Balance Sheets. To date, such cumulative currency translation adjustments have not been significant to our consolidated financial position. Our comprehensive income (loss) consists of our net income (loss) plus our foreign currency translation gains and losses and unrealized holding gains and losses on available-for-sale securities, neither of which were significant during the years ended December 31, 2019 , 2018 , and 2017 . In addition, there were no significant reclassifications out of accumulated other comprehensive loss to the statements of operations during the years ended December 31, 2019 , 2018 and 2017 . The preparation of consolidated financial statements in conformity with U.S. generally accepted accounting principles (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Accounting estimates and assumptions are inherently uncertain. Actual results could differ materially from those estimates and assumptions. Our estimates include those related to the selling prices of performance obligations and amounts of variable consideration in collaboration agreements, royalty revenue, and other assumptions required for revenue recognition as described further below; the net realizable value of inventory; the impairment of investments, goodwill and long-lived assets; contingencies, accrued clinical trial, contract manufacturing and other expenses; non-cash royalty revenue and non-cash interest expense from our liability related to our sale of future royalties; assumptions used in stock-based compensation; and ongoing litigation, among other estimates. We base our estimates on historical experience and on other assumptions that management believes are reasonable under the circumstances. These estimates form the basis for making judgments about the carrying values of assets and liabilities when these values are not readily apparent from other sources. As appropriate, we assess estimates each period, update them to reflect current information, and will generally reflect any changes in estimates in the period first identified.
Cash, Cash Equivalents, and Investments, and Fair Value of Financial Instruments	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 coupon 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	Accounts Receivable and Significant Customer Concentrations Our customers are primarily pharmaceutical and biotechnology companies that are primarily located in the U.S. and Europe and with whom we have multi-year arrangements. Our accounts receivable balance contains billed and unbilled trade receivables from product sales, milestones, other contingent payments and royalties, and cost-sharing billings from collaborative research and development agreements. For the year ended December 31, 2019 , our accounts receivable included $12.8 million under customer contracts from our collaboration partners and $24.0 million for unbilled net expense reimbursements from our collaboration partner Bristol-Myers Squibb Company (BMS). For the year ended December 31, 2018 , our accounts receivable included $24.2 million from customer contracts and $19.0 million for unbilled net expense reimbursements from BMS. We generally do not require collateral from our partners. We perform a regular review of our partners’ 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, 2019 , three partners represented 65% , 17% and 14% , respectively, of our accounts receivable. At December 31, 2018 , three different partners represented 44% , 36% and 12% , respectively, of our accounts receivable.
Inventory and Significant Supplier Concentrations	Inventory and Significant Supplier Concentrations We generally manufacture inventory upon receipt of firm purchase orders from our collaboration partners, and we may manufacture certain intermediate work-in-process materials and purchase raw materials based on purchase forecasts from our collaboration partners. Inventory includes direct materials, direct labor, and manufacturing overhead, and we determine cost on a first-in, first-out basis for raw materials and on a specific identification basis for work-in-process and finished goods. We value inventory at the lower of cost or net realizable value, and we write down defective or excess inventory to net realizable value based on historical experience or projected usage. We expense inventory related to our research and development activities when we purchase or manufacture it. Before the regulatory approval of our drug candidates, we recognize research and development expense for the manufacture of drug products that could potentially be available to support the commercial launch of our drug candidates, if approved. We are dependent on our suppliers and contract manufacturers to provide raw materials and 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, if supplies are delayed or interrupted for any reason, our ability to develop and produce our drug candidates or our ability to meet our supply obligations could be significantly impaired, which could have a material adverse effect on our business, financial condition and results of operations.
Leases	Leases On January 1, 2019, we adopted Accounting Standards Codification (ASC) 842, Leases (ASC 842). ASC 842 supersedes the guidance in ASC 840, Leases (ASC 840). Under ASC 842, an entity recognizes a right-of-use asset and a corresponding lease liability, measured as the present value of the lease payments. In our adoption, we used the package of practical expedients, which, among other things, allowed us to carry forward our historical lease classification of those leases in effect as of January 1, 2019. We present results for the year ended December 31, 2019 under ASC 842. We have not restated the results for the years ended December 31, 2018 and 2017 and our financial position as of December 31, 2018, and continue to report them under ASC 840. We determine if an arrangement contains a lease at the inception of the arrangement. Right-of-use assets represent our right to use an underlying asset for the lease term, and lease liabilities represent our obligation to make lease payments arising from the lease. We recognize operating lease right-of-use assets and liabilities at the lease commencement date based on the present value of lease payments over the expected lease term. In determining the present value of lease payments, we use our incremental borrowing rate based on the information available at the lease commencement date. However, in determining the present value of our lease payments for leases in effect when we adopted ASC 842, we used our incremental borrowing rate as of January 1, 2019. We elected the practical expedient to account for the lease and non-lease components, such as common area maintenance charges, as a single lease component for our facilities leases, and elected the short-term lease recognition exemption for our short-term leases, which allows us not to recognize lease liabilities and right-of-use assets for leases with an original term of twelve months or less. Our expected lease terms may include options to extend or terminate the lease when it is reasonably certain that we will exercise any such options. We recognize lease expense for our operating leases on a straight-line basis over the expected lease term. We have elected to recognize lease incentives, such as tenant improvement allowances, at the lease commencement date as a reduction of the right-of-use asset and lease liability until paid to us by the lessor to the extent that the lease provides a specified fixed or maximum level of reimbursement and we are reasonably certain to incur reimbursable costs at least equaling such amounts. For leases in effect as of January 1, 2019, we recognized our lease incentives as part of our transition adjustment. As a result of our adoption of ASC 842, we recorded right-of-use assets of $ 83.5 million and lease liabilities of $ 96.2 million for our facilities operating leases, with no effect on our opening balance of accumulated deficit. Please see Note 6 for additional information regarding our leases.
Long-Lived Assets	Long-Lived Assets We state property, plant and equipment at cost, net of accumulated depreciation. We capitalize major improvements and expense maintenance and repairs as incurred. We generally recognize depreciation on a straight-line basis. We depreciate manufacturing, laboratory and other equipment over their estimated useful lives of generally three to ten years , depreciate buildings over the estimated useful life of generally twenty years and amortize leasehold improvements over the shorter of the estimated useful lives or the remaining term of the related lease. Goodwill represents the excess of the price paid for another entity over the fair value of the assets acquired and liabilities assumed in a business combination. We are organized in one reporting unit and evaluate the goodwill for the Company as a whole. Goodwill has an indefinite useful life and is not amortized, but instead tested for impairment at least annually in the fourth quarter of each year using an October 1 measurement date. We assess the impairment of long-lived assets whenever events or changes in business circumstances indicate that the carrying amounts of the assets may not be fully recoverable. In the case of property, plant and equipment and right-of-use assets for our leases, we determine whether there has been an impairment by comparing the carrying value of the asset to the anticipated undiscounted net cash flows associated with the asset. If such cash flows are less than the carrying value, we write down the asset to its fair value, which may be measured as anticipated discounted net cash flows associated with the asset. In the case of goodwill impairment, we compare the carrying value of the reporting unit to its fair value, which we generally measure using market capitalization for our single reporting unit. If an impairment exists, we write down goodwill such that the carrying value of the reporting units equals its fair value.
Collaborative Arrangements	Collaborative Arrangements We enter into collaboration arrangements with pharmaceutical and biotechnology collaboration partners, under which we may grant licenses to our collaboration partners to further develop and commercialize one of our proprietary drug candidates, either alone or in combination with the collaboration partners’ compounds, or grant licenses to partners to use our technology to research and develop their own proprietary drug candidates. We may also perform research, development, manufacturing and supply activities under our collaboration agreements. Consideration under these contracts may include an upfront payment, development and regulatory milestones and other contingent payments, expense reimbursements, royalties based on net sales of approved drugs, and commercial sales milestone payments. Additionally, these contracts may provide options for the customer to purchase our proprietary PEGylation materials, drug candidates or additional contract research and development services under separate contracts. When we enter into collaboration agreements, we assess whether the arrangements fall within the scope of ASC 808, Collaborative Arrangements (ASC 808) based on whether the arrangements involve joint operating activities and whether both parties have active participation in the arrangement and are exposed to significant risks and rewards. To the extent that the arrangement falls within the scope of ASC 808, we assess whether the payments between us and our collaboration partner fall within the scope of other accounting literature. If we conclude that payments from the collaboration partner to us represent consideration from a customer, such as license fees and contract research and development activities, we account for those payments within the scope of ASC 606, Revenue from Contracts with Customers (ASC 606). However, if we conclude that our collaboration partner is not a customer for certain activities and associated payments, such as for certain collaborative research, development, manufacturing and commercial activities, we present such payments as a reduction of research and development expense or general and administrative expense, based on where we present the underlying expense. Additionally, if we reimburse our collaboration partners for these activities, we present such reimbursements as research and development expense or general and administrative expense, depending upon the nature of the underlying expense.
Revenue Recognition	Revenue Recognition For elements of those arrangements that we determine should be accounted for under ASC 606, we assess which activities in our collaboration agreements are performance obligations that should be accounted for separately and determine the transaction price of the arrangement, which includes the assessment of the probability of achievement of future milestones and other potential consideration. For arrangements that include multiple performance obligations, such as granting a license or performing contract research and development activities or participation on joint steering or other committees, we allocate upfront and milestone payments under a relative standalone selling price method. Accordingly, we develop assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. These key assumptions may include revenue forecasts, clinical development timelines and costs, discount rates and probabilities of clinical and regulatory success. Product sales Product sales are primarily derived from manufacturing and supply agreements with our customers. We have assessed our current manufacturing and supply arrangements and have generally determined that they provide the customer an option to purchase our proprietary PEGylation materials. Accordingly, we treat each purchase order as a discrete exercise of the customer’s option (i.e. a separate contract) rather than as a component of the overall arrangement. The pricing for the manufacturing and supply is generally at a fixed price and may be subject to annual producer price index (PPI) adjustments. We invoice and recognize product sales when title and risk of loss pass to the customer, which generally occurs upon shipment. Customer payments are generally due 30 days from receipt of invoice. We test our products for adherence to technical specifications 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 after achievement of the triggering event. Research and Development Services : For amounts allocated to our research and development obligations in a collaboration arrangement, we recognize revenue over time using a proportional performance model, representing the transfer of goods or services as we perform activities over the term of the agreement.
Shipping and Handling Costs	Shipping and Handling Costs We recognize costs related to shipping and handling of product to customers in cost of goods sold.
Research and Development Expense	Research and Development Expense Research and development costs are expensed as incurred and include salaries, benefits and other operating costs such as outside services, supplies and allocated overhead costs. We perform research and development for our proprietary drug candidates and technology development and for certain third parties under collaboration agreements. For our proprietary drug candidates and our internal technology development programs, we invest our own funds without reimbursement from a third party. Where we perform research and development activities under a clinical joint development collaboration, such as our collaboration with BMS, we record the cost reimbursement from our partner as a reduction to research and development expense when reimbursement amounts are due to us under the agreement. We record an accrued expense for the estimated costs of our clinical trial activities performed by third parties. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows to our vendors. Payments under the contracts depend on factors such as the achievement of certain events, successful enrollment of patients, and completion of certain clinical trial activities. We generally accrue costs associated with the start-up and reporting phases of the clinical trials ratably over the estimated duration of the start-up and reporting phases. We generally accrue costs associated with the treatment phase of clinical trials based on the estimated activities performed by our third parties. We may also accrue expenses based on the total estimated cost of the treatment phase on a per patient basis and expense the per patient cost ratably over the estimated patient treatment period based on patient enrollment in the trials. In specific circumstances, such as for certain time-based costs, we recognize clinical trial expenses using a methodology that we consider to be more reflective of the timing of costs incurred. We record an accrued expense for the estimated unbilled 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. We capitalize advance payments for goods or services that will be used or rendered for future research and development activities and recognize expense as the related goods are delivered or the services performed. We base our estimates on the best information available at the time. However, additional information may become available to us which may allow us to make a more accurate estimate in future periods. In this event, we may be required to record adjustments to research and development expenses in future periods when the actual level of activity becomes more certain. We consider such increases or decreases in cost as changes in estimates and reflect them in research and development expenses in the period identified.
Stock-Based Compensation	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, including but not limited to, our stock price volatility over the term of the awards, and actual and projected employee stock option exercise behaviors. Because our employee stock options have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models may not provide a reliable single measure of the fair value of our employee stock options or common stock purchased under the ESPP. The 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 grant date fair value 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. We recognize stock-based compensation expense for purchases under the ESPP over the respective six-month purchase period. We report expense amounts in cost of goods sold, research and development expense, and general and administrative expense based on the function of the applicable employee. Stock-based compensation charges are non-cash charges and have no effect on our reported cash flows.
Net Income (Loss) Per Share	Net Income (Loss) Per Share For all periods presented in the Consolidated Statements of Operations, the net income (loss) available to common stockholders is equal to the reported net income (loss). We calculate basic net income (loss) per share based on the weighted-average number of common shares outstanding during the periods presented and calculate diluted net income (loss) per share based on the weighted-average number of shares of common stock outstanding, including potentially dilutive securities, which consist of common shares underlying stock options and restricted stock units (RSUs). For 2019 and 2017 , basic and diluted net loss per share are the same due to our net losses and the requirement to exclude potentially dilutive securities which would have an antidilutive effect on net loss per share. We excluded weighted average outstanding stock options and RSUs totaling 17.9 million and 20.6 million for 2019 and 2017 , respectively. 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.
Income Taxes	Income Taxes We account for income taxes under the liability method. Under this method, we determine deferred tax assets and liabilities based on differences between the financial reporting and tax reporting bases of assets and liabilities, measured using enacted tax rates and laws that we expect to be in effect when we expect the differences to reverse. Realization of deferred tax assets is dependent upon future earnings, the timing and amount of which are uncertain. We record a valuation allowance against deferred tax assets to reduce their carrying value to an amount that is more likely than not to be realized. When we establish or reduce the valuation allowance related to the deferred tax assets, our provision for income taxes will increase or decrease, respectively, in the period we make such determination. We utilize a two-step approach to recognize and measure uncertain tax positions. The first step is to evaluate the tax position for recognition by determining if the weight of available evidence indicates that it is more likely than not that the position will be sustained upon tax authority examination, including resolution of related appeals or litigation processes, if any. The second step is to measure the tax benefit as the largest amount of benefit, determined on a cumulative probability basis, that is more than 50% likely of being realized upon ultimate settlement.
Comprehensive income (loss)	Comprehensive income (loss) Comprehensive income (loss) is the change in stockholders’ equity from transactions and other events and circumstances other than those resulting from investments by stockholders and distributions to stockholders. Our other comprehensive income (loss) includes net income (loss), gains and losses from the foreign currency translation of the assets and liabilities of our India and UK subsidiaries, and unrealized gains and losses on investments in available-for-sale securities.
Recently Adopted Accounting Pronouncements and Recent Accounting Pronouncements	Recently Adopted Accounting Pronouncements In December 2019, the FASB issued ASU 2019-12 - Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes (ASU 2019-12). ASU 2019-12 created an exception to the incremental approach for intraperiod tax allocation when there is a loss from continuing operations and income or a gain from other items (for example, discontinued operations or other comprehensive income). Under the historical guidance, in this situation, an entity would record an income tax provision from other items, such as unrealized gains on available-for-sale reported in other comprehensive income, with an offsetting income tax benefit in continuing operations. Under ASU 2019-12, an entity would record no income tax provision. We elected to adopt ASU 2019-12 effective January 1, 2019 on a prospective basis in accordance with the guidance. Because we reported a net loss and unrealized gains on available-for-sale securities for our quarterly reporting periods during 2019 and accordingly recorded a tax provision pursuant to the legacy guidance, we have recast such results for our Selected Quarterly Financial Data in Note 15 under ASU 2019-12. As a result, we eliminated the tax benefit in continuing operations and tax provision in other comprehensive income, which totaled $1.3 million for the nine months ended September 30, 2019. 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 . 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. Accordingly, we continue to report our results for the year ended December 31, 2017 under the historical revenue guidance ASC 605. Our transition adjustment totaled $12.7 million , and included $10.7 million related to the recognition of royalty revenue and $2.0 million for the reduction of deferred revenue related to one of our collaboration arrangements. Recent Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13: Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The guidance modifies the measurement and recognition of credit losses for most financial assets and certain other instruments. The amendment updates the guidance for measuring and recording credit losses on financial assets measured at amortized cost by replacing the “incurred loss” model with an “expected loss” model. Accordingly, we will present these financial assets at the net amount we expect to collect. The amendment also requires that we record credit losses related to available-for-sale debt securities as an allowance through net income rather than reducing the carrying amount under the current, other-than-temporary-impairment model. ASU 2016-13 is effective in the first quarter of 2020. Early adoption is permitted. We do not expect that adoption will have a material effect on our Consolidated Financial Statements. 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.
Liability Related to Sale of Future Royalties	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.

Cash and Investments in Marke_2

Cash and Investments in Marketable Securities (Tables)	12 Months Ended
	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Cash and Investments in Marketable Securities, Including Cash Equivalents	Cash and investments in marketable securities, including cash equivalents, are as follows (in thousands): Estimated Fair Value at December 31, December 31, Cash and cash equivalents $ 96,363 $ 194,905 Short-term investments 1,228,499 1,140,445 Long-term investments 279,119 582,889 Total cash and investments in marketable securities $ 1,603,981 $ 1,918,239
Portfolio of Cash and Investments in Marketable Securities	Our portfolio of cash and investments in marketable securities includes (in thousands): Fair Value Hierarchy Level Estimated Fair Value at December 31, December 31, Corporate notes and bonds 2 $ 1,132,182 $ 1,288,986 Corporate commercial paper 2 375,473 498,048 Obligations of U.S. government agencies 2 — 12,977 Available-for-sale investments 1,507,655 1,800,011 Money market funds 1 83,546 105,656 Certificate of deposit N/A 6,951 6,760 Cash N/A 5,829 5,812 Total cash and investments in marketable securities $ 1,603,981 $ 1,918,239

Inventory (Tables)

Inventory (Tables)	12 Months Ended
	Dec. 31, 2019
Inventory Disclosure [Abstract]
Inventory	Inventory consists of the following (in thousands): December 31, 2019 2018 Raw materials $ 1,673 $ 1,846 Work-in-process 8,267 6,403 Finished goods 2,725 3,132 Total inventory $ 12,665 $ 11,381

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2019
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Property, plant and equipment consists of the following (in thousands): December 31, 2019 2018 Building and leasehold improvements $ 93,097 $ 77,771 Laboratory equipment 36,623 33,806 Computer equipment and software 26,910 23,395 Manufacturing equipment 22,030 21,339 Furniture, fixtures, and other 9,662 7,959 Depreciable property, plant and equipment at cost 188,322 164,270 Less: accumulated depreciation (127,875 ) (120,507 ) Depreciable property, plant and equipment, net 60,447 43,763 Construction-in-progress 4,552 5,088 Property, plant and equipment, net $ 64,999 $ 48,851

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2019
Leases [Abstract]
Lease, Cost	The components of lease costs, which we include in operating expenses in our Condensed Consolidated Statements of Operations, were as follows (in thousands): Year Ended December 31, 2019 2018 2017 Operating lease cost $ 14,697 $ 7,972 $ 4,515 Variable lease cost 6,408 4,497 3,077 Total lease costs $ 21,105 $ 12,469 $ 7,592
Future Minimum Lease Payments for Operating Leases	As of December 31, 2019 , the maturities of our operating lease liabilities were as follows (in thousands): Year ending December 31, 2020 $ 14,571 2021 19,219 2022 19,832 2023 20,461 2024 21,110 2025 and thereafter 118,058 Total lease payments 213,251 Less: portion representing interest (54,741 ) Less: lease incentives (3,264 ) Operating lease liabilities 155,246 Less: current portion (12,516 ) Operating lease liabilities, less current portion $ 142,730
Schedule of Future Minimum Rental Payments for Operating Leases	Under the historical guidance of ASC 840, our deferred rent balance at December 31, 2018 totaled $9.3 million and our future minimum lease payments for our operating leases at December 31, 2018 were 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_2

Liability Related to the Sale of Future Royalties (Tables)	12 Months Ended
	Dec. 31, 2019
Liability Related To Sale Of Potential Future Royalties [Abstract]
Summary of Liability Related to Potential Future Royalties	The following table shows the activity within the liability account during the year ended December 31, 2019 and for the period from the inception of the royalty transaction on February 24, 2012 (inception) to December 31, 2019 (in thousands): Year ended Period from Liability related to the sale of future royalties—beginning balance $ 84,810 $ — Proceeds from sale of future royalties — 124,000 Payments from Nektar to RPI — (10,000 ) Non-cash CIMZIA ® and MIRCERA ® royalty revenue (36,303 ) (207,142 ) Non-cash interest expense recognized 25,044 166,693 Liability related to the sale of future royalties – ending balance 73,551 73,551 Less: unamortized transaction costs (1,531 ) (1,531 ) Liability related to the sale of future royalties, net $ 72,020 $ 72,020

License and Collaboration Agr_2

License and Collaboration Agreements (Tables)	12 Months Ended
	Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
License, Collaboration and Other Revenue	In accordance with our collaboration agreements, we recognized license, collaboration and other revenue as follows (in thousands): Year Ended December 31, Partner Agreement 2019 2018 2017 Bristol-Myers Squibb NKTR-214 $ — $ 1,059,768 $ — Eli Lilly and Company NKTR-358 7,019 11,634 130,087 Amgen, Inc. Neulasta ® 5,000 5,000 5,000 Baxalta Incorporated / Takeda Hemophilia, including ADYNOVATE ® and ADYNOVI™ 378 20,328 11,443 Ophthotech Corporation(1) Fovista ® — — 19,123 Bayer Healthcare LLC(1) BAY41-6551 (Amikacin Inhale) — — 17,931 AstraZeneca AB MOVANTIK ® and MOVENTIG ® — — 4,600 Other 4,578 535 22,781 License, collaboration and other revenue $ 16,975 $ 1,097,265 $ 210,965 _______________________________________________________________ (1)
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, 2019 (in thousands): For the year ended Deferred revenue—December 31, 2018 $ 24,636 Recognition of previously unearned revenue (16,565 ) Deferred revenue—December 31, 2019 $ 8,071

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Compensation Expense	We recognize total stock-based compensation expense in our Condensed Consolidated Statements of Operations as follows (in thousands): Year Ended December 31, 2019 2018 2017 Cost of goods sold $ 4,294 $ 4,629 $ 2,333 Research and development 63,224 56,193 21,252 General and administrative 32,277 27,279 13,030 Total stock-based compensation $ 99,795 $ 88,101 $ 36,615
Black-Scholes Option-Pricing Model Assumptions Used to Calculate Fair Value of Employee Stock Options	The following table lists the Black-Scholes option-pricing model assumptions used to calculate the fair value of employee and director stock options, as well as the resulting grant-date fair value: Year Ended December 31, 2019 2018 2017 Average risk-free interest rate 1.8 % 2.8 % 2.0 % Dividend yield 0.0 % 0.0 % 0.0 % Average volatility factor 62.2 % 61.0 % 54.2 % Weighted-average expected life 5.6 years 5.1 years 5.3 years Weighted-average grant-date fair value of options granted $ 12.25 $ 29.86 $ 20.08
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, 2018 15,930 $ 26.18 Options granted 1,842 21.86 Options exercised (1,629 ) 11.68 Options forfeited & canceled (1,258 ) 49.91 Outstanding at December 31, 2019 14,885 $ 25.23 4.31 $ 73,134 Exercisable at December 31, 2019 9,938 20.79 3.14 $ 66,707 _______________________________________________________________ (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, 2019
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, 2018 3,320 $ 41.57 Granted 3,189 23.32 Vested and released (1,159 ) 36.33 Forfeited and canceled (415 ) 43.19 Balance at December 31, 2019 4,935 $ 30.85 $ 106,506

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2019
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, 2019 2018 2017 Domestic $ (441,494 ) $ 680,423 $ (97,938 ) Foreign 1,440 2,302 1,862 Income (loss) before provision for income taxes $ (440,054 ) $ 682,725 $ (96,076 )
Provision for Income Taxes	The provision for income taxes consists of the following (in thousands): Year Ended December 31, 2019 2018 2017 Current: Federal $ — $ — $ — State 139 699 1 Foreign 495 620 580 Total Current 634 1,319 581 Deferred: Federal — — — State — — — Foreign (21 ) 93 35 Total Deferred (21 ) 93 35 Provision for income taxes $ 613 $ 1,412 $ 616
Income Tax Provision Related to Continuing Operations	Income tax provision related to continuing operations differs from the amount computed by applying the statutory income tax rate of 21% for the years ended December 31, 2019 and 2018 and 35% for the year ended December 31, 2017 to pretax income (loss) as follows (in thousands): Year Ended December 31, 2019 2018 2017 Income tax expense (benefit) at federal statutory rate $ (92,411 ) $ 143,372 $ (33,627 ) Research credits (10,511 ) (17,295 ) (8,038 ) Sale of future royalties (7,624 ) (6,995 ) (8,236 ) Stock-based compensation (672 ) (66,716 ) (20,665 ) Premium on equity issuance — (12,551 ) — Change in valuation allowance 104,440 (46,885 ) (186,124 ) Non-cash interest expense on liability related to sale of future royalties 5,259 4,451 6,604 Non-deductible officers’ compensation 737 3,182 2,547 Tax law changes 23 45 248,155 Other 1,372 804 — Provision for income taxes $ 613 $ 1,412 $ 616
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. Significant components of our deferred tax assets for federal and state income taxes are as follows (in thousands): December 31, 2019 2018 Deferred tax assets: Net operating loss carryforwards $ 399,361 $ 300,693 Research and other credits 128,015 116,955 Operating lease liabilities 36,907 — Stock-based compensation 30,875 21,518 Property, plant and equipment 5,021 2,124 Capitalized research expenses 3,705 8,072 Reserves and accruals 2,934 8,066 Deferred revenue 1,908 4,467 Deferred tax assets before valuation allowance 608,726 461,895 Valuation allowance for deferred tax assets (575,087 ) (460,455 ) Total deferred tax assets 33,639 1,440 Operating lease right-of-use assets (31,718 ) — Other (1,725 ) (1,270 ) Total deferred tax liabilities (33,443 ) (1,270 ) Net deferred tax assets $ 196 $ 170
Unrecognized Tax Benefits	We have the following activity relating to unrecognized tax benefits (in thousands): December 31, 2019 2018 2017 Beginning balance $ 27,419 $ 20,483 $ 18,413 Tax positions related to current year Additions: Federal 1,365 2,019 1,206 State 48,493 3,645 1,666 Reductions — — — Tax positions related to prior year Additions: Federal — 669 — State 277 603 — Foreign — — — Reductions (144 ) — (802 ) Settlements — — — Lapses in statute of limitations — — — Ending balance $ 77,410 $ 27,419 $ 20,483

Segment Reporting (Tables)

Segment Reporting (Tables)	12 Months Ended
	Dec. 31, 2019
Segment Reporting [Abstract]
Revenue by Geographic Area	The following table sets forth revenue by geographic area (in thousands): Year Ended December 31, 2019 2018 2017 United States $ 27,093 $ 1,090,794 $ 190,810 Rest of World 87,524 102,529 116,901 Total revenue $ 114,617 $ 1,193,323 $ 307,711

Selected Quarterly Financial _2

Selected Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2019
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Data	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, 2019 Year Ended December 31, 2018 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Product sales $ 4,398 $ 4,346 $ 5,558 $ 5,815 $ 6,295 $ 5,863 $ 4,256 $ 4,360 Total revenue $ 28,222 $ 23,315 $ 29,218 $ 33,862 $ 38,018 $ 1,087,717 $ 27,762 $ 39,826 Cost of goods sold $ 5,440 $ 5,018 $ 4,927 $ 5,989 $ 6,646 $ 5,522 $ 4,783 $ 7,461 Research and development expenses $ 118,463 $ 106,686 $ 99,048 $ 110,369 $ 99,424 $ 88,334 $ 102,895 $ 108,883 Operating income (loss) $ (120,687 ) $ (110,970 ) $ (98,740 ) $ (109,638 ) $ (86,739 ) $ 973,600 $ (98,634 ) $ (100,295 ) Net income (loss) (1) $ (119,632 ) $ (110,286 ) $ (98,585 ) $ (112,164 ) $ (95,792 ) $ 971,460 $ (96,143 ) $ (98,212 ) Net income (loss) per share(1) (2) Basic $ (0.69 ) $ (0.63 ) $ (0.56 ) $ (0.64 ) $ (0.60 ) $ 5.67 $ (0.56 ) $ (0.57 ) Diluted $ (0.69 ) $ (0.63 ) $ (0.56 ) $ (0.64 ) $ (0.60 ) $ 5.33 $ (0.56 ) $ (0.57 ) _______________________________________________________________ (1) As discussed in Note 1, in the fourth quarter of 2019, we adopted ASU 2019-12, effective January 1, 2019, which affected previously reported amounts of net loss and net loss per share for the first three quarters of 2019. We have recast such amounts for the effects of adoption. (2) 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 S_3

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) shares in Millions	Jan. 01, 2019USD ($)	Jan. 01, 2018USD ($)	Sep. 30, 2019USD ($)	Dec. 31, 2019USD ($)Reporting_UnitCustomershares	Dec. 31, 2018USD ($)Customershares	Dec. 31, 2017shares
Organization And Summary Of Significant Accounting Policies [Line Items]
Cash and investments in marketable securities				$ 1,603,981,000	$ 1,918,239,000
Senior secured notes				250,000,000
Contract with customer, asset, reclassified to receivable				12,800,000	24,200,000
Net expense reimbursements from collaboration partner				$ 24,000,000	$ 19,000,000
Number of customers accounted for major accounts receivable | Customer				3	3
Percentage of accounts receivable customers one				65.00%	44.00%
Percentage of accounts receivable customers two				17.00%	36.00%
Percentage of accounts receivable customers three				14.00%	12.00%
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
Other comprehensive income (loss), tax			$ 1,300,000
Operating lease right-of-use assets				$ 134,177,000	$ 0
Operating lease, liability				$ 155,246,000
Deferred rent					$ 9,300,000
Accounting Standards Update 2016-02
Organization And Summary Of Significant Accounting Policies [Line Items]
Operating lease right-of-use assets	$ 83,500,000
Operating lease, liability	96,200,000
Cumulative effect on retained earnings, net of tax	$ 0
ASC 606
Organization And Summary Of Significant Accounting Policies [Line Items]
Adjustment to retained earnings		$ 12,700,000
Reduction of deferred revenue		(2,000,000)
ASC 606 | Royalty | Calculated under Revenue Guidance in Effect before Topic 606
Organization And Summary Of Significant Accounting Policies [Line Items]
Adjustment to retained earnings		$ 10,700,000
Shares of Common Stock Underlying Outstanding Stock Options
Organization And Summary Of Significant Accounting Policies [Line Items]
Weighted average antidilutive securities excluded from computation of earnings per share | shares					3.3
Stock Options and Restricted Stock Units
Organization And Summary Of Significant Accounting Policies [Line Items]
Weighted average antidilutive securities excluded from computation of earnings per share | shares				17.9		20.6
Manufacturing equipment | Minimum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives				3 years
Manufacturing equipment | Maximum
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives				10 years
Buildings
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives				20 years

Cash and Investments in Marke_3

Cash and Investments in Marketable Securities - Cash and Investments in Marketable Securities, Including Cash Equivalents (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	$ 96,363	$ 194,905
Short-term investments	1,228,499	1,140,445
Long-term investments	279,119	582,889
Total cash and investments in marketable securities	$ 1,603,981	$ 1,918,239

Cash and Investments in Marke_4

Cash and Investments in Marketable Securities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and Investments in Marketable Securities [Line Items]
Sales of investments	$ 0	$ 11,963,000	$ 37,549,000
Level 1 to level 2 transfers	0	0
Level 2 to level 1 transfers	0	0
Letter of credit	$ 6,800,000	$ 6,600,000
Maximum
Cash and Investments in Marketable Securities [Line Items]
Long term investment maturity period	2 years

Cash and Investments in Marke_5

Cash and Investments in Marketable Securities - Portfolio of Cash and Investments in Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	$ 1,507,655	$ 1,800,011
Cash	5,829	5,812
Total cash and investments in marketable securities	1,603,981	1,918,239
Corporate Notes and Bonds | Fair Value Hierarchy Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	1,132,182	1,288,986
Corporate Commercial Paper | Fair Value Hierarchy Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	375,473	498,048
Obligations of U.S. government agencies | Fair Value Hierarchy Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	0	12,977
Money Market Funds | Fair Value Hierarchy Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	83,546	105,656
Certificates of Deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	$ 6,951	$ 6,760

Inventory - Inventory (Detail)

Inventory - Inventory (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 1,673	$ 1,846
Work-in-process	8,267	6,403
Finished goods	2,725	3,132
Total inventory	$ 12,665	$ 11,381

Property, Plant and Equipment -

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	$ 188,322	$ 164,270
Less: accumulated depreciation	(127,875)	(120,507)
Depreciable property, plant and equipment, net	60,447	43,763
Construction-in-progress	4,552	5,088
Property, plant and equipment, net	64,999	48,851
Building and leasehold improvements
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	93,097	77,771
Laboratory equipment
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	36,623	33,806
Computer equipment and software
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	26,910	23,395
Manufacturing equipment
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	22,030	21,339
Furniture, fixtures, and other
Property, Plant and Equipment [Line Items]
Depreciable property, plant and equipment at cost	$ 9,662	$ 7,959

Property, Plant and Equipment_2

Property, Plant and Equipment - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Depreciation and amortization expenses		$ 11	$ 8.8	$ 12.6
Costs related to terminated manufacturing obligations	$ 0.9
Manufacturing Equipment
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 - Addition

Senior Secured Notes - Additional Information (Detail) - USD ($)	Oct. 05, 2015	Dec. 31, 2019
Secured Notes [Line Items]
Senior secured notes, principal amount		$ 250,000,000
Actual days outstanding		360 days
Senior Notes | 7.75% Senior Secured Notes Due October 2020
Secured Notes [Line Items]
Senior secured notes, principal amount	$ 250,000,000
Senior secured notes, interest rate	7.75%
Issuance costs	$ 8,900,000
Debt discount on transaction and facility fees	8,700,000
Unamortized debt discount and issuance costs		$ 1,300,000
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 | 7.75% Senior Secured Notes Due October 2020 | Level 3
Secured Notes [Line Items]
Senior notes fair value		$ 252,600,000
Senior Notes | 7.75% Senior Secured Notes Redemption Date After October 5, 2019
Secured Notes [Line Items]
Debt redemption price percentage of principal amount	100.00%

Leases - Additional Information

Leases - Additional Information (Detail) $ in Thousands	1 Months Ended			12 Months Ended
	Jun. 30, 2018ft²	May 31, 2018ft²	Aug. 31, 2017ft²extension_period	Dec. 31, 2019USD ($)ft²	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2019	Aug. 31, 2019ft²
Leases [Line Items]
Operating lease right-of-use assets				$ 134,177	$ 0
Operating lease, liability				155,246
Right-of-use assets recognized in exchange for operating lease liabilities				57,691	0	$ 0
Operating lease cost				14,697	7,972	4,515
Operating lease, payments				$ 8,400
Weighted average remaining lease term				10 years 1 month 6 days
Weighted average discount rate, percent							5.90%
Deferred rent					9,300
Variable lease cost				$ 6,408	4,497	3,077
Total lease costs				$ 21,105	$ 12,469	$ 7,592
ARE-San Francisco No. 19, LLC | Mission Bay Lease
Leases [Line Items]
Lease space | ft²			148,263
Number of consecutive 5 year terms to extend lease | extension_period			2
Lease extension term			5 years
Leased space delivered | ft²				13,907
Operating lease right-of-use assets				$ 6,700
Operating lease, liability				6,700
Additional space required to be leased in the future | ft²			4,940
Kilroy Realty Finance Partnership, L.P | Third Street Lease
Leases [Line Items]
Lease space | ft²		135,936						67,105
Leased space delivered | ft²	1,726	67,105
Right-of-use assets recognized in exchange for operating lease liabilities				$ 51,000

Leases Leases - Future Minimum

Leases Leases - Future Minimum Lease Payments for Operating Leases (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
2020	$ 14,571
2021	19,219
2022	19,832
2023	20,461
2024	21,110
2025 and thereafter	118,058
Total lease payments	213,251
Less: portion representing interest	(54,741)
Less: lease incentives	(3,264)
Operating lease liabilities	155,246
Less: current portion	(12,516)	$ 0
Operating lease liabilities, less current portion	$ 142,730	$ 0

Leases - Future Minimum Lease P

Leases - Future Minimum Lease Payments for Operating Leases Prior To Adoption of ASC 842 (Detail) $ in Thousands	Dec. 31, 2019USD ($)
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_3

Liability Related to the Sale of Future Royalties - Additional Information (Detail) - USD ($) $ in Thousands	Feb. 24, 2012	Feb. 24, 2012	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2019
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								$ 36,303	$ 33,308	$ 30,531		$ 207,142
Non-cash interest expense on liability related to sale of future royalties								$ 25,044	$ 21,196	$ 18,869		$ 166,693
Annual interest rate					19.50%	18.70%	17.60%				17.00%
Prospective interest rate					38.00%	29.00%	21.00%
Purchase and Sale Agreement with RPI
Liability Related to the Sale of Future Royalties [Line Items]
Proceeds from sale of royalty rights	$ 124,000	$ 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_4

Liability Related to the Sale of Future Royalties - Summary of Liability Related to Potential Future Royalties (Detail) - USD ($) $ in Thousands	12 Months Ended			94 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Liability Related To The Sale Of Future Royalties [Roll Forward]
Liability related to the sale of future royalties—beginning balance	$ 84,810			$ 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	(36,303)	$ (33,308)	$ (30,531)	(207,142)
Non-cash interest expense recognized	25,044	21,196	$ 18,869	166,693
Liability related to the sale of future royalties – ending balance	73,551	84,810		73,551
Less: unamortized transaction costs	(1,531)			(1,531)
Liability related to the sale of future royalties, net	$ 72,020	$ 82,911		$ 72,020

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) - USD ($)	Dec. 31, 2019	Dec. 31, 2018
Loss Contingencies [Line Items]
Purchase commitments related to contract manufacturing, clinical development and certain other items	$ 25,800,000
Putative Securities Class Action
Loss Contingencies [Line Items]
Litigation matters, liabilities	0
Indemnification Obligation
Loss Contingencies [Line Items]
Litigation matters, liabilities	0	$ 0
Merger and Acquisition Related Claims | Maximum
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	5,000,000
Securities Related Claims
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	5,000,000
Non-Securities Related Claims
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	$ 1,500,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Detail) - USD ($)	Jun. 26, 2018	Apr. 03, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Sale of common stock (in shares)				8,285,000
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			19,817,000
Number of shares available for issuance under equity compensation plans			9,145,000
Common stock, shares authorized (in shares)			300,000,000	300,000,000
Maximum 401(k) per employee, percentage of annual salary			60.00%
Matching 401(k) employer contribution, maximum amount			$ 6,000
Compensation expense in connection with 401(k) retirement plan			$ 3,500,000	$ 2,800,000	$ 1,600,000
Change in control severance payment period for executives			12 months
Change in control severance payment period for employees			6 months
Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock, shares authorized (in shares)			2,500,000
Percentage of purchase price of stock			85.00%
2017 Performance Incentive Plan
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
2012 Plan
Class of Stock [Line Items]
Number of additional shares available for award grants			7,000,000
Common Shares
Class of Stock [Line Items]
Sale of common stock (in shares)		8,284,600
Common stock, shares reserved for issuance in equity compensation plans			28,962,018
Employee | 2017 Performance Incentive Plan | Shares of Common Stock Underlying Outstanding Stock Options
Class of Stock [Line Items]
Service period for stock-based compensation award granted			4 years
Employee | 2017 Performance Incentive Plan | Restricted Stock Units (RSU)
Class of Stock [Line Items]
Service period for stock-based compensation award granted			3 years
Director | 2017 Performance Incentive Plan | Shares of Common Stock Underlying Outstanding Stock Options
Class of Stock [Line Items]
Service period for stock-based compensation award granted			1 year
Director | 2017 Performance Incentive Plan | Restricted Stock Units (RSU)
Class of Stock [Line Items]
Service period for stock-based compensation award granted			1 year

License and Collaboration Agr_3

License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 16,975	$ 1,097,265	$ 210,965
Collaboration agreements completion date	Dec. 31, 2017
Bristol-Myers Squibb | NKTR-214
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 0	1,059,768	0
Eli Lilly and Company | NKTR-358
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	7,019	11,634	130,087
Amgen, Inc. | Neulasta
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	5,000	5,000	5,000
Baxalta Incorporated / Takeda | Hemophilia, Including ADYNOVATE and ADYNOVITM
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	378	20,328	11,443
Ophthotech Corporation | Fovista
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	0	19,123
Bayer Healthcare LLC | BAY41-6551 (Amikacin Inhale)
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	0	17,931
AstraZeneca AB | MOVANTIK and MOVENTIG
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	0	4,600
Other
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 4,578	$ 535	$ 22,781

License and Collaboration Agr_4

License and Collaboration Agreements - Additional Information (Detail) - USD ($)

Feb. 13, 2018

Jan. 01, 2018

Aug. 23, 2017

Apr. 30, 2018

Oct. 31, 2017

Sep. 30, 2017

Jan. 31, 2017

Sep. 30, 2016

Mar. 31, 2016

Jun. 30, 2014

Oct. 31, 2010

Dec. 31, 2019

Sep. 30, 2019

Jun. 30, 2019

Mar. 31, 2019

Dec. 31, 2018

Sep. 30, 2018

Jun. 30, 2018

Mar. 31, 2018

Dec. 31, 2017

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Dec. 31, 2015

Dec. 31, 2013

Dec. 31, 2007

Jan. 09, 2020

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Performance obligation recognized

$ 77,500,000

$ 95,300,000

Potential future additional payments for development milestones

$ 1,700,000,000

1,700,000,000

Deferred revenue, current portion

5,517,000

$ 13,892,000

5,517,000

13,892,000

Deferred revenue, less current portion

2,554,000

10,744,000

2,554,000

10,744,000

Upfront and milestone payments received from license agreements

10,000,000

Accounts receivable

36,802,000

43,213,000

36,802,000

43,213,000

Development milestones received

16,565,000

Deferred revenue

8,071,000

24,636,000

8,071,000

24,636,000

Revenue recognized from contracts with customers

33,862,000

$ 29,218,000

$ 23,315,000

$ 28,222,000

39,826,000

$ 27,762,000

$ 1,087,717,000

$ 38,018,000

114,617,000

1,193,323,000

$ 307,711,000

bempegaldesleukin | Nektar's

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Upfront and milestone payments received from license agreements

$ 1,000,000,000

Maximum total additional cash payments receivable upon achievement of certain development and regulatory milestones

1,400,000,000

bempegaldesleukin | Nektar's | Maximum

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Eligible additional cash payments receivable upon achievement of certain sales milestones

$ 350,000,000

ADYNOVATE

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Sales milestone revenue

10,000,000

BMS Collaboration Agreement | bempegaldesleukin | Nektar's

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Global commercialization profits and losses sharing percentage

65.00%

Percentage of sharing production costs

65.00%

BMS Collaboration Agreement | bempegaldesleukin | Nektar's | Opdivo

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Percentage of sharing development costs

32.50%

BMS Collaboration Agreement | bempegaldesleukin | Nektar's | Opdivo and Yervoy

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Percentage of sharing development costs

22.00%

NKTR-358 | Nektar's

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Deferred revenue

1,300,000

$ 1,300,000

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

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Percentage of upfront payment, market access milestones, royalties and sales milestones

40.00%

Eli Lilly | NKTR-358

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Percentage of sharing in Phase 2 development costs

75.00%

Bristol-Myers Squibb | Purchase Agreement

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Shares issued (in shares)

8,284,600

Sale of stock consideration received

$ 850,000,000

Bristol-Myers Squibb | bempegaldesleukin | Research and development

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Reimbursement of expenses

$ 105,400,000

62,500,000

7,800,000

Bristol-Myers Squibb | BMS Collaboration Agreement

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Accounts receivable

24,000,000

19,000,000

24,000,000

19,000,000

Bristol-Myers Squibb | BMS Collaboration Agreement | Purchase Agreement

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Total consideration received under agreements

1,850,000,000

Estimated fair value of shares

$ 790,200,000

Closing date price of common stock (in usd per share)

$ 99.36

Remaining amount allocated to transaction price

$ 1,059,800,000

Potential future development, regulatory and sales milestones

$ 1,800,000,000

Bristol-Myers Squibb | BMS Collaboration Agreement | bempegaldesleukin

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Global commercialization profits and losses sharing percentage

35.00%

Percentage of sharing production costs

35.00%

Amount recognized for granting licenses

1,059,800,000

Bristol-Myers Squibb | BMS Collaboration Agreement | bempegaldesleukin | Opdivo

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Percentage of sharing development costs

67.50%

Bristol-Myers Squibb | BMS Collaboration Agreement | bempegaldesleukin | Opdivo and Yervoy

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Percentage of sharing development costs

78.00%

Bristol-Myers Squibb | Clinical Trial Agreement | bempegaldesleukin

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Percentage of out-of-pocket costs to be reimbursed by partner

50.00%

Baxalta Incorporated / Takeda

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Potential future additional payments for development milestones

10,000,000

$ 10,000,000

Baxalta Incorporated / Takeda | Hemophilia

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Received under right to sublicense agreement

$ 12,000,000

Baxalta Incorporated / Takeda | Hemophilia | European Union

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Upfront and milestone payments received from license agreements

10,000,000

Additional upfront and milestone payments recognized from license agreements

10,000,000

Eli Lilly and Company | NKTR-358 | Phase 1 Clinical Development

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Received upfront and milestone payment

17,600,000

Eli Lilly and Company | NKTR-358 | Drug Product Development

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Received upfront and milestone payment

6,500,000

Eli Lilly and Company | NKTR-358 | Maximum

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Potential future additional development and regulatory milestones

$ 250,000,000

Eli Lilly and Company | NKTR-358 | Nektar's

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Percentage of regulatory milestones payments will be reduced under certain conditions

50.00%

Percentage of regulatory milestones payments will be reduced if conditions occur

75.00%

Eli Lilly and Company | NKTR-358 | Nektar's | Maximum

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Percentage of funding phase 3 development costs on an indication by indication basis borne

25.00%

Eli Lilly and Company | NKTR-358 | Nektar's | Minimum

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Percentage of funding phase 3 development costs on an indication by indication basis borne

0.00%

Eli Lilly and Company | NKTR-358 | License

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Received upfront and milestone payment

$ 125,900,000

Eli Lilly and Company | NKTR-358 | License | ASC 606

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Revenue recognized from contracts with customers

$ 125,900,000

Amgen, Inc.

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Received upfront and milestone payment

$ 50,000,000

Amgen, Inc. | ASC 606

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Deferred revenue

4,200,000

4,200,000

Ophthotech Corporation

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Advance payment from collaboration partner

$ 12,700,000

Ophthotech Corporation | Reagent Shipments

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Advance payment from collaboration partner for reagent shipments

$ 10,400,000

Ophthotech Corporation | Minimum Purchase Requirement

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Advance payment from collaboration partner

2,300,000

Ophthotech Corporation | Fovista

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Recognition of remaining deferred revenue

$ 18,000,000

Ophthotech Corporation | Fovista | Novartis Pharma AG

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Received upfront and milestone payment

$ 19,800,000

Bayer Healthcare LLC

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Received upfront and milestone payment

$ 40,000,000

Bayer Healthcare LLC | Performance-based Milestone Payments

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Received upfront and milestone payment

$ 30,000,000

Recognition of remaining deferred revenue

$ 16,800,000

AstraZeneca AB | MOVANTIK and MOVENTIG | Upfront Payment Arrangement

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Received upfront and milestone payment

$ 385,000,000

AstraZeneca AB | AstraZeneca-Kirin

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Deferred revenue

0

0

Received upfront and milestone payment

$ 4,600,000

Percentage of upfront payment, market access milestone payments, royalties and sales milestone payments from sublicense agreement retained by our collaboration partner

60.00%

AstraZeneca AB

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Potential future additional payments for development milestones

40,000,000

40,000,000

Deferred revenue

4,000,000

4,000,000

Terminated Partnership

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Deferred revenue

$ 2,000,000

$ 2,000,000

Milestone One | Subsequent Event | BMS Collaboration Agreement | bempegaldesleukin | Nektar's

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Potential future additional payments for development milestones

$ 25,000,000

Milestone Two | Subsequent Event | BMS Collaboration Agreement | bempegaldesleukin | Nektar's

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Potential future additional payments for development milestones

25,000,000

Milestone Three | Subsequent Event | BMS Collaboration Agreement | bempegaldesleukin | Nektar's

Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]

Potential future additional payments for development milestones

$ 75,000,000

License and Collaboration Agr_5

License and Collaboration Agreements - Changes in Deferred Revenue Balance from Collaboration Agreements (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue, Beginning balance	$ 24,636
Recognition of previously unearned revenue	(16,565)
Deferred revenue, Ending balance	$ 8,071

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 99,795	$ 88,101	$ 36,615
Cost of goods sold
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	4,294	4,629	2,333
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	63,224	56,193	21,252
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 32,277	$ 27,279	$ 13,030

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation costs	$ 213.7
Recognized over a weighted-average period	1 year 9 months
Dividend yield	0.00%	0.00%	0.00%
Weighted-average grant-date fair value (per share)	$ 12.25	$ 29.86	$ 20.08
Total intrinsic value of options exercised	$ 30.6	$ 303.4	$ 84
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield	0.00%
Restricted Stock Units (RSU)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock vested	$ 32.4	$ 80.4	$ 22.3

Stock-Based Compensation - Blac

Stock-Based Compensation - Black-Scholes Option-Pricing Model Assumptions Used to Calculate Fair Value of Employee Stock Options (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Average risk-free interest rate	1.80%	2.80%	2.00%
Dividend yield	0.00%	0.00%	0.00%
Average volatility factor	62.20%	61.00%	54.20%
Average weighted average expected life	5 years 7 months 6 days	5 years 1 month 6 days	5 years 3 months 18 days
Weighted-average grant-date fair value (per share)	$ 12.25	$ 29.86	$ 20.08

Stock-Based Compensation - St_2

Stock-Based Compensation - Stock Option Activity Under Equity Incentive Plans (Detail) - Stock Options $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares, outstanding, beginning balance (in shares) | shares	15,930
Number of shares, options granted (in shares) | shares	1,842
Number of shares, options exercised (in shares) | shares	(1,629)
Number of shares, options forfeited and canceled (in shares) | shares	(1,258)
Number of shares, outstanding, ending balance (in shares) | shares	14,885
Number of shares, exercisable (in shares) | shares	9,938
Weighted-Average Exercise Price per Share, outstanding, beginning balance (in dollars per share) | $ / shares	$ 26.18
Weighted-Average Exercise Price per Share, options granted (in dollars per share) | $ / shares	21.86
Weighted-Average Exercise Price per Share, options exercised (in dollars per share) | $ / shares	11.68
Weighted-Average Exercise Price per Share, options forfeited and canceled (in dollars per share) | $ / shares	49.91
Weighted-Average Exercise Price per Share, outstanding, ending balance (in dollars per share) | $ / shares	25.23
Weighted-Average Exercise Price per Share, exercisable (in dollars per share) | $ / shares	$ 20.79
Weighted-Average Remaining Contractual Life, outstanding	4 years 3 months 21 days
Weighted-Average Remaining Contractual Life, exercisable	3 years 1 month 20 days
Aggregate Intrinsic Value, outstanding | $	$ 73,134
Aggregate Intrinsic Value, exercisable | $	$ 66,707

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Unit Award Activity (Detail) - Restricted Stock Units (RSU) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units Issued, Beginning balance (in shares) | shares	3,320
Granted (in shares) | shares	3,189
Vested and released (in shares) | shares	(1,159)
Forfeited and canceled (in shares) | shares	(415)
Units Issued, Ending balance (in shares) | shares	4,935
Weighted Average Grant Date Fair Value, Beginning balance (in dollars per share) | $ / shares	$ 41.57
Weighted Average Grant Date Fair Value, Granted (in dollars per share) | $ / shares	23.32
Weighted Average Grant Date Fair Value, Vested and released (in dollars per share) | $ / shares	36.33
Weighted Average Grant Date Fair Value, Forfeited and canceled (in dollars per share) | $ / shares	43.19
Weighted Average Grant Date Fair Value, Ending balance (in dollars per share) | $ / shares	$ 30.85
Aggregate Intrinsic Value, Ending balance | $	$ 106,506

Income Taxes - Income (Loss) Be

Income Taxes - Income (Loss) Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Domestic	$ (441,494)	$ 680,423	$ (97,938)
Foreign	1,440	2,302	1,862
Income (loss) before provision for income taxes	$ (440,054)	$ 682,725	$ (96,076)

Income Taxes - Provision for In

Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current:
Federal	$ 0	$ 0	$ 0
State	139	699	1
Foreign	495	620	580
Total Current	634	1,319	581
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	(21)	93	35
Total Deferred	(21)	93	35
Provision for income taxes	$ 613	$ 1,412	$ 616

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes Disclosure [Line Items]
Statutory income tax rate		21.00%	21.00%
Valuation allowance, increase (decrease) amount	$ 114,600,000	$ (35,700,000)	$ (169,300,000)
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	10,511,000	17,295,000	8,038,000
Federal orphan drug credits	$ 17,700,000
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
Income Taxes Disclosure [Line Items]
Net operating loss carryforward for income tax	1,721,700,000
Income tax research credits	94,800,000
State
Income Taxes Disclosure [Line Items]
Net operating loss carryforward for income tax	1,221,300,000
Income tax research credits	$ 49,400,000

Income Taxes - Income Tax Provi

Income Taxes - Income Tax Provision Related to Continuing Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income tax expense (benefit) at federal statutory rate	$ (92,411)	$ 143,372	$ (33,627)
Research credits	(10,511)	(17,295)	(8,038)
Sale of future royalties	(7,624)	(6,995)	(8,236)
Stock-based compensation	(672)	(66,716)	(20,665)
Premium on equity issuance	0	(12,551)	0
Change in valuation allowance	104,440	(46,885)	(186,124)
Non-cash interest expense on liability related to sale of future royalties	5,259	4,451	6,604
Non-deductible officers’ compensation	737	3,182	2,547
Tax law changes	23	45	248,155
Other	1,372	804	0
Provision for income taxes	$ 613	$ 1,412	$ 616

Income Taxes - Significant Comp

Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Net operating loss carryforwards	$ 399,361	$ 300,693
Research and other credits	128,015	116,955
Operating lease liabilities	36,907	0
Stock-based compensation	30,875	21,518
Property, plant and equipment	5,021	2,124
Capitalized research expenses	3,705	8,072
Reserves and accruals	2,934	8,066
Deferred revenue	1,908	4,467
Deferred tax assets before valuation allowance	608,726	461,895
Valuation allowance for deferred tax assets	(575,087)	(460,455)
Total deferred tax assets	33,639	1,440
Operating lease right-of-use assets	(31,718)	0
Other	(1,725)	(1,270)
Total deferred tax liabilities	(33,443)	(1,270)
Net deferred tax assets	$ 196	$ 170

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 27,419	$ 20,483	$ 18,413
Reductions	0	0	0
Reductions	(144)	0	(802)
Settlements	0	0	0
Lapses in statute of limitations	0	0	0
Ending balance	77,410	27,419	20,483
Federal
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Tax positions related to current year, Additions	1,365	2,019	1,206
Tax positions related to prior year, Additions	0	669	0
State
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Tax positions related to current year, Additions	48,493	3,645	1,666
Tax positions related to prior year, Additions	277	603	0
Foreign
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Tax positions related to prior year, Additions	$ 0	$ 0	$ 0

Segment Reporting - Additional

Segment Reporting - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2019USD ($)Segment	Dec. 31, 2018USD ($)	Dec. 31, 2017
Segment Reporting Information [Line Items]
Number of operating business segment | Segment	1
Property, plant and equipment, net	$ 64,999	$ 48,851
United States
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 59,700	$ 42,900
Percentage of net book value of property and equipment	92.00%	88.00%
India
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 5,300	$ 5,900
Percentage of net book value of property and equipment	8.00%	12.00%
Revenue | BMS | Customer Concentration Risk
Segment Reporting Information [Line Items]
Percentage revenue from customers		89.00%
Revenue | Eli Lilly & Company | Customer Concentration Risk
Segment Reporting Information [Line Items]
Percentage revenue from customers			42.00%
Revenue | UCB | Customer Concentration Risk
Segment Reporting Information [Line Items]
Percentage revenue from customers	28.00%		12.00%
Revenue | Baxalta Incorporated / Takeda | Customer Concentration Risk
Segment Reporting Information [Line Items]
Percentage revenue from customers	19.00%
Revenue | AstraZeneca AB | Customer Concentration Risk
Segment Reporting Information [Line Items]
Percentage revenue from customers	17.00%

Segment Reporting - Revenue by

Segment Reporting - Revenue by Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue by geographic area
Total revenue	$ 33,862	$ 29,218	$ 23,315	$ 28,222	$ 39,826	$ 27,762	$ 1,087,717	$ 38,018	$ 114,617	$ 1,193,323	$ 307,711
United States | Reportable Geographical Components
Revenue by geographic area
Total revenue									27,093	1,090,794	190,810
Non-US | Reportable Geographical Components
Revenue by geographic area
Total revenue									$ 87,524	$ 102,529	$ 116,901

Subsequent Event (Details)

Subsequent Event (Details) - USD ($) $ in Millions	Jan. 14, 2020	Dec. 31, 2019
Subsequent Event [Line Items]
Purchase commitments related to contract manufacturing, clinical development and certain other items		$ 25.8
NKTR - 181 | Subsequent Event
Subsequent Event [Line Items]
Write off of prepayment	$ 19.7
Purchase commitments related to contract manufacturing, clinical development and certain other items	45
Purchase Commitment, Remaining Maximum Amount Committed	$ 50

Selected Quarterly Financial _3

Selected Quarterly Financial Data - Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Selected Quarterly Financial Data [Line Items]
Total revenue	$ 33,862	$ 29,218	$ 23,315	$ 28,222	$ 39,826	$ 27,762	$ 1,087,717	$ 38,018	$ 114,617	$ 1,193,323	$ 307,711
Cost of goods sold	5,989	4,927	5,018	5,440	7,461	4,783	5,522	6,646	21,374	24,412	30,547
Research and development expenses	110,369	99,048	106,686	118,463	108,883	102,895	88,334	99,424	434,566	399,536	268,461
Operating income (loss)	(109,638)	(98,740)	(110,970)	(120,687)	(100,295)	(98,634)	973,600	(86,739)	(440,035)	687,932	(59,642)
Net income (loss) (1)	$ (112,164)	$ (98,585)	$ (110,286)	$ (119,632)	$ (98,212)	$ (96,143)	$ 971,460	$ (95,792)	$ (440,667)	$ 681,313	$ (96,692)
Net income (loss) per share
Basic ( in dollars per share)	$ (0.64)	$ (0.56)	$ (0.63)	$ (0.69)	$ (0.57)	$ (0.56)	$ 5.67	$ (0.60)	$ (2.52)	$ 4.02	$ (0.62)
Diluted (in dollars per share)	$ (0.64)	$ (0.56)	$ (0.63)	$ (0.69)	$ (0.57)	$ (0.56)	$ 5.33	$ (0.60)	$ (2.52)	$ 3.78	$ (0.62)
Product Sales
Selected Quarterly Financial Data [Line Items]
Total revenue	$ 5,815	$ 5,558	$ 4,346	$ 4,398	$ 4,360	$ 4,256	$ 5,863	$ 6,295	$ 20,117	$ 20,774	$ 32,688

Uncategorized Items - nktr-2019

Label	Element	Value
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 12,577,000
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 12,577,000