Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2017	Feb. 22, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2017
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 Common Stock, Shares Outstanding		160,922,921
Entity Public Float			$ 3,028,667,056

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 4,762	$ 59,640
Short-term investments	291,370	329,462
Accounts receivable, net of allowance of nil at December 31, 2017 and 2016	5,014	15,678
Inventory	10,726	11,109
Other current assets	14,948	10,063
Total current assets	326,820	425,952
Long-term investments	57,088	0
Property, plant and equipment, net	47,463	65,601
Goodwill	76,501	76,501
Other assets	994	817
Total assets	508,866	568,871
Current liabilities:
Accounts payable	4,782	2,816
Accrued compensation	8,263	18,280
Accrued clinical trial expenses	9,461	7,958
Other accrued expenses	10,064	4,711
Interest payable	4,198	4,198
Liability related to refundable upfront payment	0	12,500
Deferred revenue, current portion	18,949	14,352
Other current liabilities	446	7,407
Total current liabilities	56,163	72,222
Senior secured notes, net	245,207	243,464
Liability related to the sale of future royalties, net	94,655	105,950
Deferred revenue, less current portion	19,021	51,887
Other long-term liabilities	5,992	7,223
Total liabilities	421,038	480,746
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares designated, issued or outstanding at December 31, 2017 or 2016	0	0
Common stock, $0.0001 par value; 300,000 shares authorized; 159,524 shares and 153,212 shares issued and outstanding at December 31, 2017 and 2016, respectively	15	15
Capital in excess of par value	2,207,865	2,111,483
Accumulated other comprehensive loss	(2,111)	(2,363)
Accumulated deficit	(2,117,941)	(2,021,010)
Total stockholders’ equity	87,828	88,125
Total liabilities and stockholders’ equity	$ 508,866	$ 568,871

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Allowance for accounts receivable	$ 0	$ 0
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares designated	0	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000,000	300,000,000
Common stock, shares issued	159,524,000	153,212,000
Common stock, shares outstanding	159,524,000	153,212,000

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Product sales	$ 32,688	$ 55,354	$ 40,155
Royalty revenue	33,527	19,542	2,967
Non-cash royalty revenue related to sale of future royalties	30,531	30,158	22,058
License, collaboration and other revenue	210,965	60,382	165,604
Total revenue	307,711	165,436	230,784
Operating costs and expenses:
Cost of goods sold	30,547	30,215	34,102
Research and development	268,461	203,801	182,787
General and administrative	52,364	44,275	43,266
Impairment of equipment and other costs for terminated program	15,981	0	0
Total operating costs and expenses	367,353	278,291	260,155
Loss from operations	(59,642)	(112,855)	(29,371)
Non-operating income (expense):
Interest expense	(22,085)	(22,468)	(18,282)
Non-cash interest expense on liability related to sale of future royalties	(18,869)	(19,712)	(20,619)
Loss on extinguishment of debt	0	0	(14,079)
Interest income and other income (expense), net	4,520	2,387	1,680
Total non-operating expense, net	(36,434)	(39,793)	(51,300)
Loss before provision for income taxes	(96,076)	(152,648)	(80,671)
Provision for income taxes	616	876	506
Net loss	$ (96,692)	$ (153,524)	$ (81,177)
Basic and diluted net loss per share	$ (0.62)	$ (1.10)	$ (0.61)
Weighted average shares outstanding used in computing basic and diluted net loss per share	155,953	139,596	132,458

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (96,692)	$ (153,524)	$ (81,177)
Other comprehensive income (loss):
Net unrealized gain (loss) on available-for-sale investments, net of tax	(533)	79	(226)
Net foreign currency translation gain (loss)	785	(272)	(377)
Other comprehensive income (loss), net of tax	252	(193)	(603)
Comprehensive loss	$ (96,440)	$ (153,717)	$ (81,780)

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Shares [Member]	Capital in Excess of Par Value [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]	Accumulated Deficit [Member]
Beginning Balance at Dec. 31, 2014	$ 36,332	$ 13	$ 1,824,195	$ (1,567)	$ (1,786,309)
Beginning Balance, Shares at Dec. 31, 2014		131,216
Shares issued under equity compensation plans	32,208	$ 0	32,208	0	0
Shares issued under equity compensation plans, Shares		4,073
Stock-based compensation	19,669	$ 0	19,669	0	0
Other comprehensive loss	(603)	0	0	(603)	0
Net loss	(81,177)	0	0	0	(81,177)
Ending Balance at Dec. 31, 2015	6,429	$ 13	1,876,072	(2,170)	(1,867,486)
Ending Balance, Shares at Dec. 31, 2015		135,289
Sale of common stock, net of issuance costs	189,276	$ 2	189,274	0	0
Sale of common stock, Shares		14,950
Shares issued under equity compensation plans	20,287	$ 0	20,287	0	0
Shares issued under equity compensation plans, Shares		2,973
Stock-based compensation	25,850	$ 0	25,850	0	0
Other comprehensive loss	(193)	0	0	(193)	0
Net loss	(153,524)	0	0	0	(153,524)
Ending Balance at Dec. 31, 2016	88,125	$ 15	2,111,483	(2,363)	(2,021,010)
Ending Balance, Shares at Dec. 31, 2016		153,212
Shares issued under equity compensation plans	59,528	$ 0	59,528	0	0
Shares issued under equity compensation plans, Shares		6,312
Stock-based compensation	36,615	$ 0	36,615	0	0
Other comprehensive loss	252	0	239	252	(239)
Net loss	(96,692)	0	0	0	(96,692)
Ending Balance at Dec. 31, 2017	$ 87,828	$ 15	$ 2,207,865	$ (2,111)	$ (2,117,941)
Ending Balance, Shares at Dec. 31, 2017		159,524

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net loss	$ (96,692)	$ (153,524)	$ (81,177)
Adjustments to reconcile net loss to net cash used in operating activities:
Non-cash royalty revenue related to sale of future royalties	(30,531)	(30,158)	(22,058)
Non-cash interest expense on liability related to sale of future royalties	18,869	19,712	20,619
Stock-based compensation	36,615	25,850	19,669
Depreciation and amortization	14,741	15,351	12,855
Loss from redemption premium and incremental interest on 12% senior secured notes	0	0	12,500
Write-off of deferred financing costs on 12% senior secured notes	0	0	1,579
Impairment of equipment from terminated program	15,081	0	0
Other non-cash transactions	(881)	(2,185)	(2,365)
Changes in operating assets and liabilities:
Accounts receivable, net	10,664	4,269	(16,340)
Inventory	383	237	1,606
Other assets	(4,800)	(312)	(825)
Accounts payable	2,074	518	(412)
Accrued compensation	(10,017)	12,282	249
Accrued clinical trial expenses	1,503	(262)	512
Other accrued expenses	5,774	191	(2,278)
Interest payable	0	0	(2,719)
Liability related to refundable upfront payment	(12,500)	12,500	0
Deferred revenue	(28,269)	(17,615)	(17,530)
Other liabilities	(2,428)	(3,878)	3,032
Net cash used in operating activities	(80,414)	(117,024)	(73,083)
Cash flows from investing activities:
Purchases of investments	(404,425)	(334,659)	(297,608)
Maturities of investments	347,743	253,682	226,923
Sales of investments	37,549	4,969	42,544
Release of restricted cash	0	0	25,000
Purchases of property, plant and equipment	(9,676)	(6,392)	(11,195)
Net cash used in investing activities	(28,809)	(82,400)	(14,336)
Cash flows from financing activities:
Payment of capital lease obligations	(5,131)	(5,945)	(5,187)
Proceeds from shares issued under equity compensation plans	59,522	20,287	32,208
Issuance of common stock, net of issuance costs	0	189,276	0
Proceeds from issuance of 7.75% senior secured notes, net of issuance costs	0	0	241,262
Repayment of 12% senior secured notes	0	0	(125,000)
Payment of redemption premium and incremental interest on 12% senior secured notes	0	0	(12,500)
Net cash provided by financing activities	54,391	203,618	130,783
Effect of exchange rates on cash and cash equivalents	(46)	(124)	(159)
Net increase (decrease) in cash and cash equivalents	(54,878)	4,070	43,205
Cash and cash equivalents at beginning of year	59,640	55,570	12,365
Cash and cash equivalents at end of year	4,762	59,640	55,570
Supplemental disclosure of cash flow information:
Cash paid for interest	20,116	20,589	20,225
Cash paid for income taxes	$ 556	$ 757	$ 860

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Summary of Significant Accounting Policies	Note 1 — Organization and Summary of Significant Accounting Policies Organization We are a research-based biopharmaceutical company headquartered in San Francisco, California and incorporated in Delaware. We are developing a pipeline of drug candidates that utilize our advanced polymer conjugate technology platforms, which are designed to enable the development of new molecular entities that target known mechanisms of action. Our research and development pipeline of new investigational drugs includes treatments for cancer, autoimmune disease and chronic pain. Our research and development activities have required significant ongoing investment to date and are expected to continue to require significant investment. As a result, 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, 2017, we had approximately $353.2 million in cash and investments in marketable securities and had debt of $250.0 million in principal of senior secured notes due in October 2020. Basis of Presentation, Principles of Consolidation and Use of Estimates Our consolidated financial statements include the financial position, results of operations and cash flows of our wholly-owned subsidiaries: Nektar Therapeutics (India) Private Limited and Nektar Therapeutics UK Limited. All intercompany accounts and transactions have been eliminated in consolidation. Our Consolidated Financial Statements are denominated in U.S. dollars. Accordingly, changes in exchange rates between the applicable foreign currency and the U.S. dollar will affect the translation of each foreign subsidiary’s financial results into U.S. dollars for purposes of reporting our consolidated financial results. Translation gains and losses are included in accumulated other comprehensive income (loss) in the stockholders’ equity section of the Consolidated Balance Sheets. To date, such cumulative translation adjustments have not been significant to our consolidated financial position. Aggregate gross foreign currency transaction gains (losses) recorded in operations for the years ended December 31, 2017, 2016, and 2015 were not significant. The preparation of consolidated financial statements in conformity with U.S. generally accepted accounting principles (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Accounting estimates and assumptions are inherently uncertain. Actual results could differ materially from those estimates and assumptions. Our estimates include those related to estimated selling prices of deliverables in collaboration agreements, estimated periods of performance, the net realizable value of inventory, the impairment of investments, the impairment of goodwill and long-lived assets, contingencies, accrued clinical trial expenses, estimated non-cash royalty revenue and non-cash interest expense from our liability related to our sale of future royalties, stock-based compensation, and ongoing litigation, among other estimates. We base our estimates on historical experience and on other assumptions that management believes are reasonable under the circumstances. These estimates form the basis for making judgments about the carrying values of assets and liabilities when these values are not readily apparent from other sources. As appropriate, estimates are assessed each period and updated to reflect current information and any changes in estimates will generally be reflected in the period first identified. Reclassifications Certain items previously reported in specific financial statement captions have been reclassified to conform to the current period presentation, including as a result of the adoption of new accounting guidance related to the classification of deferred tax assets described below. Such reclassifications do not materially impact previously reported revenue, operating loss, net loss, total assets, liabilities or stockholders’ equity. Cash, Cash Equivalents, and Investments, and Fair Value of Financial Instruments We consider all investments in marketable securities with an original maturity of three months or less when purchased to be cash equivalents. 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, are classified as short-term investments. Investments in securities with remaining maturities of over one year are classified 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. Interest and dividends on securities classified as available-for-sale, as well as amortization of premiums and accretion of discounts to maturity, are included in interest income. Realized gains and losses and declines in value of available-for-sale securities judged to be other-than-temporary, if any, are included 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 U.S. government obligations, money market instruments and funds, and corporate bonds and places restrictions on maturities and concentrations by type and issuer. Accounts Receivable and Significant Customer Concentrations Our customers are primarily pharmaceutical and biotechnology companies that are located in the U.S. and Europe and with whom we have multi-year arrangements. Our accounts receivable balance contains billed and unbilled trade receivables from product sales, milestones, other contingent payments and royalties, as well as time and materials based billings from collaborative research and development agreements. When appropriate, we provide for an allowance for doubtful accounts by reserving for specifically identified doubtful accounts. We generally do not require collateral from our customers. We perform a regular review of our customers’ credit risk and payment histories, including payments made subsequent to year-end. We have not experienced significant credit losses from our accounts receivable. At December 31, 2017, four different customers represented 43%, 20%, 19% and 14%, respectively, of our accounts receivable. At December 31, 2016, three different customers represented 39%, 32%, and 13%, respectively, of our accounts receivable. Inventory and Significant Supplier Concentrations Inventory is generally manufactured upon receipt of firm purchase orders from our collaboration partners. Inventory includes direct materials, direct labor, and manufacturing overhead and cost is determined on a first-in, first-out basis. Inventory is valued at the lower of cost or net realizable value and defective or excess inventory is written down to net realizable value based on historical experience or projected usage. Inventory related to our research and development activities is expensed when purchased. We are dependent on our suppliers and contract manufacturers to provide raw materials, drugs and devices of appropriate quality and reliability and to meet applicable contract and regulatory requirements. In certain cases, we rely on single sources of supply of one or more critical materials. Consequently, in the event that supplies are delayed or interrupted for any reason, our ability to develop and produce our drug candidates or our ability to meet our supply obligations could be significantly impaired, which could have a material adverse effect on our business, financial condition and results of operations. Long-Lived Assets Property, plant and equipment are stated at cost. Major improvements are capitalized, while maintenance and repairs are expensed when incurred. Manufacturing, laboratory and other equipment are depreciated using the straight-line method generally over estimated useful lives of three to ten years. Buildings are depreciated using the straight-line method generally over the estimated useful life of twenty years. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful life or the remaining term of the lease. Goodwill represents the excess of the price paid for another entity over the fair value of the assets acquired and liabilities assumed in a business combination. We are organized in one reporting unit and evaluate the goodwill for the Company as a whole. Goodwill has an indefinite useful life and is not amortized, but instead tested for impairment at least annually in the fourth quarter of each year using an October 1 measurement date. We assess the impairment of long-lived assets whenever events or changes in business circumstances indicate that the carrying amounts of the assets may not be fully recoverable. When such events occur, we determine whether there has been an impairment in value by comparing the carrying value of the asset with its fair value, as measured by the anticipated undiscounted net cash flows associated with the asset. In the case of goodwill impairment, market capitalization is generally used as the measure of fair value. If an impairment in value exists, the asset is written down to its estimated fair value. Revenue Recognition Our revenue is derived from our arrangements with pharmaceutical and biotechnology collaboration partners and may result from one or more of the following: upfront and license fees, payments for contract research and development, milestone and other contingent payments, manufacturing and supply payments, and royalties. Our performance obligations under our collaborations may include licensing our intellectual property, manufacturing and supply obligations, and research and development obligations. In order to account for the multiple-element arrangements, we identify the deliverables included within the arrangement and evaluate which deliverables represent separate units of accounting. Analyzing the arrangement to identify deliverables requires the use of judgment, and each deliverable may be an obligation to deliver goods or services, a right or license to use an asset, or another performance obligation. Revenue is recognized separately for each identified unit of accounting when the basic revenue recognition criteria are met: there is persuasive evidence that an arrangement exists, delivery has occurred, the price is fixed or determinable, and collection is reasonably assured. At the inception of each new multiple-element arrangement or the material modification of an existing multiple-element arrangement, we allocate all consideration received under multiple-element arrangements to all units of accounting based on the relative selling price method, generally based on our best estimate of selling price (ESP). The objective of ESP is to determine the price at which we would transact a sale if the product or service was sold on a stand-alone basis. We determine ESP for the elements in our collaboration arrangements by considering multiple factors including, but not limited to, technical complexity of the performance obligation and similarity of elements to those performed under previous arrangements. Since we apply significant judgment in arriving at the ESPs, any material change in our estimates would significantly affect the allocation of the total consideration to the different elements of a multiple element arrangement. Product sales Product sales are primarily derived from fixed price manufacturing and supply agreements with our collaboration partners. Our products are tested for adherence to technical specifications prior to shipment, accordingly, we have not experienced any significant returns from our customers. Royalty revenue Generally, we are entitled to royalties from our collaboration partners based on the net sales of their approved drugs that are marketed and sold in one or more countries where we hold royalty rights. We recognize royalty revenue when the cash is received or when the royalty amount to be received is estimable and collection is reasonably assured. With respect to the non-cash royalties related to our sale of future royalties described in Note 7, revenue is recognized when estimable, otherwise, revenue is recognized during the period in which the related royalty report is received, which generally occurs in the quarter after the applicable product sales are made. License, collaboration and other revenue The amount of upfront fees and other payments received by us in license and collaboration arrangements that are allocated to continuing performance obligations, such as manufacturing and supply obligations, is deferred and generally recognized ratably over our expected performance period under each respective arrangement. We make our best estimate of the period over which we expect to fulfill our performance obligations, which may include technology transfer assistance, research activities, clinical development activities, and manufacturing activities from research and development through the commercialization of the product. Given the uncertainties of these collaboration arrangements, significant judgment is required to determine the duration of the performance period and this estimate is periodically re-evaluated. Upon the termination of each of our license and collaboration arrangements and if no additional services are required to be performed by us, all non-refundable, non-creditable amounts previously deferred from the arrangement are recognized as revenue. Contingent consideration received from the achievement of a substantive milestone is recognized in its entirety in the period in which the milestone is achieved, which we believe is consistent with the substance of our performance under our various license and collaboration agreements. A milestone is defined as an event (i) that can only be achieved based in whole or in part either on the entity’s performance or on the occurrence of a specific outcome resulting from the entity’s performance, (ii) for which there is substantive uncertainty at the date the arrangement is entered into that the event will be achieved, and (iii) that would result in additional payments being due to the entity. A milestone is substantive if the consideration earned from the achievement of the milestone is consistent with our performance required to achieve the milestone or the increase in value to the collaboration resulting from our performance, relates solely to our past performance, and is reasonable relative to all of the other deliverables and payments within the arrangement. Our license and collaboration agreements with our partners provide for payments to us upon the achievement of development milestones, such as the completion of clinical trials or regulatory submissions, approvals by regulatory authorities, and commercial launches of drugs. Given the challenges inherent in developing and obtaining regulatory approval for drug products and in achieving commercial launches, there was substantial uncertainty whether any such milestones would be achieved at the time of execution of these licensing and collaboration agreements. In addition, we evaluated whether the development milestones met the remaining criteria to be considered substantive. As a result of our analysis, we consider our remaining development milestones under all of our license and collaboration agreements to be substantive and, accordingly, we recognize as revenue payments received from each milestone only if and as such milestone is achieved. Our license and collaboration agreements with certain partners also provide for contingent payments to us based solely upon the performance of the respective partner. For such contingent amounts, we recognize the payments as revenue when earned under the applicable contract, which is generally upon completion of performance by the respective partner, provided that collection is reasonably assured. Our license and collaboration agreements with our partners also provide for payments to us upon the achievement of specified sales volumes of approved drugs. We consider these payments to be similar to royalty payments and we recognize such sales-based payments upon achievement of such sales volumes, provided that collection is reasonably assured. Shipping and Handling Costs We recognize costs related to shipping and handling of product to customers in cost of goods sold. Research and Development Expense Research and development costs are expensed as incurred and include salaries, benefits and other operating costs such as outside services, supplies and allocated overhead costs. We perform research and development for our proprietary drug candidates and technology development and for certain third parties under collaboration agreements. For our proprietary drug candidates and our internal technology development programs, we invest our own funds without reimbursement from a third party. Where we perform research and development activities under a clinical joint development collaboration, such as our collaboration with Bristol-Myers Squibb, we record the 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 accruals for the estimated costs of our clinical trial activities performed by third parties. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows to our vendors. Payments under the contracts depend on factors such as the achievement of certain events, successful enrollment of patients, and completion of certain clinical trial activities. We generally accrue costs associated with the start-up and reporting phases of the clinical trials ratably over the estimated duration of the start-up and reporting phases. We generally accrue costs associated with the treatment phase of clinical trials based on the total estimated cost of the treatment phase on a per patient basis and we expense the per patient cost ratably over the estimated patient treatment period based on patient enrollment in the trials. In specific circumstances, such as for certain time-based costs, we recognize clinical trial expenses using a methodology that we consider to be more reflective of the timing of costs incurred. Advance payments for goods or services that will be used or rendered for future research and development activities are capitalized as prepaid expenses and recognized as expense as the related goods are delivered or the related services are performed. We base our estimates on the best information available at the time. However, additional information may become available to us which may allow us to make a more accurate estimate in future periods. In this event, we may be required to record adjustments to research and development expenses in future periods when the actual level of activity becomes more certain. Such increases or decreases in cost are generally considered to be changes in estimates and will be reflected in research and development expenses in the period identified. Stock-Based Compensation Stock-based compensation arrangements include stock option grants and restricted stock unit (RSU) awards under our equity incentive plans, as well as shares issued under our Employee Stock Purchase Plan (ESPP), through which employees may purchase our common stock at a discount to the market price. We use the Black-Scholes option pricing model for the respective grant to determine the estimated fair value of the option on the date of grant (grant date fair value) and the estimated fair value of common stock purchased under the ESPP. The Black-Scholes option pricing model requires the input of highly subjective assumptions. These variables include, but are not limited to, our stock price volatility over the term of the awards, and actual and projected employee stock option exercise behaviors. Because our employee stock options have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models may not provide a reliable single measure of the fair value of our employee stock options or common stock purchased under the ESPP. The fair value of an RSU is equal to the closing price of our common stock on the grant date. Management will continue to assess the assumptions and methodologies used to calculate the estimated fair value of stock-based compensation. Circumstances may change and additional data may become available over time, which could result in changes to these assumptions and methodologies, and which could materially impact our fair value determination. We expense the value of the portion of the option or award on a straight line basis over the requisite service periods in our Consolidated Statements of Operations and recognize forfeitures of options and awards as they occur. For options and awards that vest upon the achievement of performance milestones, we estimate the vesting period based on our evaluation of the probability of achievement of each respective milestone and the related estimated date of achievement. Stock-based compensation expense for purchases under the ESPP is recognized over the respective six-month purchase period. Expense amounts are recorded in cost of goods sold, research and development expense, and general and administrative expense based on the function of the applicable employee. Stock-based compensation charges are non-cash charges and as such have no impact on our reported cash flows. Net Loss Per Share Basic net loss per share is calculated based on the weighted-average number of common shares outstanding during the periods presented. For all periods presented in the Consolidated Statements of Operations, 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 anti-dilutive effect on net loss per share. During 2017, 2016 and 2015, potentially dilutive securities consisted of common shares underlying outstanding stock options and RSUs. There were weighted average outstanding stock options and RSUs of 20.6 million, 19.9 million and 21.1 million during the years ended December 31, 2017, 2016 and 2015, respectively. Income Taxes We account for income taxes under the liability method. Under this method, deferred tax assets and liabilities are determined based on differences between the financial reporting and tax reporting bases of assets and liabilities and are measured using enacted tax rates and laws that are expected to be in effect when the differences are expected 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 such determination is made. 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 loss Comprehensive 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) is comprised of net loss, gains and losses from the foreign currency translation of the assets and liabilities of our India and UK subsidiaries, and unrealized gains and losses on investments in available-for-sale securities. Adoption of New Accounting Principle In March 2016, the Financial Accounting Standards Board (FASB) issued guidance to simplify several aspects of employee share-based payment accounting, including forfeitures, income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. This guidance was effective for our interim and annual periods beginning January 1, 2017. As a result of the adoption of this guidance, as of January 1, 2017, we recorded a $0.2 million charge to our accumulated deficit in our Consolidated Balance Sheet related to our election to recognize forfeitures of awards as they occur. In addition, prior to adoption of this guidance, tax attributes related to stock option windfall deductions were not recorded until they resulted in a reduction of cash tax payable. As of December 31, 2016, the excluded windfall deductions for federal and state purposes were $20.6 million and $9.8 million, respectively. Upon adoption, we recognized the excluded windfall deductions as a deferred tax asset on a tax-effected basis with a corresponding increase in the valuation allowance. In November 2015, the FASB issued guidance to require that deferred tax assets and liabilities be classified as noncurrent on the balance sheet. Previous guidance required deferred tax assets and liabilities to be separated into current and noncurrent amounts on the balance sheet. Accordingly, as of January 1, 2017, we reclassified $0.3 million from other current assets to our other assets balance. This reclassification was applied retrospectively to these balances in our Consolidated Balance Sheet as of December 31, 2016. Recent Accounting Pronouncements In May 2014, the FASB issued guidance codified in Accounting Standards Codification (ASC) 606, Revenue Recognition — Revenue from Contracts with Customers, which supersedes the guidance in ASC 605, Revenue Recognition, and is effective for public companies for annual and interim periods beginning after December 15, 2017. The FASB has issued numerous updates that provide clarification on a number of specific issues as well as requiring additional disclosures. We plan to adopt the standard in the first quarter of 2018 using the modified retrospective method. The new guidance requires the application of a five-step model to determine the amount and timing of revenue to be recognized and requires that we recognize revenue in a manner that reasonably reflects the delivery of our goods or services to customers in return for expected consideration. To achieve this core principle, the guidance provides the following steps: (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when (or as) the entity satisfies a performance obligation. Under ASC 606, companies may need to use more judgment and make more estimates than under ASC 605 in the application of this five-step process. We are continuing to assess the impact of the new guidance on our accounting policies and procedures and are evaluating the new requirements as applied to existing collaboration agreements, both in terms of the cumulative adjustment to opening accumulated deficit and our subsequent recognition of revenue. Since each collaboration agreement is unique, we will separately assess each agreement (see Note 10 for a discussion of our existing collaboration agreements) under the new standard. We anticipate that the adoption of ASC 606 will have the following impact to our revenue recognition for a collaboration agreement: (i) Changes in revenue recognition for distinct licenses of functional intellectual property may result in a timing difference of revenue recognition between the current literature and ASC 606. For certain of our arrangements, the value associated with the licenses and certain other deliverables have been assessed as one unit of accounting and recognized over a period of time in which services are rendered or made available to our customer pursuant to revenue recognition guidance in effect for such arrangements at the time such arrangements commenced. For certain other arrangements, under current ASC 605 guidance, we identified the value of the license as a separate unit of accounting and recognize revenue upon issuance of the license. Under ASC 606, we may continue to recognize revenue for such licenses upon delivery of the license. (ii) For other consideration, including milestone payments or contingent payments from our collaboration partners, under our current accounting policy, we recognize such payments as revenue in the period that the payment-triggering event occurred or is achieved. The new revenue standard, however, may require us to recognize these payments before the payment-triggering event is completely achieved, subject to management’s assessment of whether it is probable that the triggering event will be achieved and that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. (iii) We will recognize revenue for sales-based royalties and commercial sales-based milestones in the period of the related sale based on estimates, rather than recording them as reported by the customer. We currently estimate that, upon adoption on January 1, 2018, we will record an adjustment to decrease our accumulated deficit by approximately $11.0 million to $13.0 million for amounts that would be recognized as of December 31, 2017 under ASC 606, but are not recognized under the current ASC 605 guidance. This estimated adjustment primarily consists of approximately $11.0 million for the accrual of royalties due to us related to net sales in the three months ended December 31, 2017 that we would have recognized in 2018 under current guidance. The estimated adjustment also includes up to approximately $2.0 million related to the recognition of the unamortized portion of upfront payment amounts under ASC 606 that are required to be deferred as of December 31, 2017 under current guidance. We will finalize our assessments in the first quarter of 2018 as we adopt ASC 606. In February 2016, the FASB issued guidance to amend a number of aspects of lease accounting, including requiring lessees to recognize almost all leases with a term greater than one year as a right-of-use asset and corresponding liability, measured at the present value of the lease payments. The guidance will become effective for us beginning in the first quarter of 2019 and is required to be adopted using a modified retrospective approach. Early adoption is permitted. We are currently evaluating the impact of the adoption of this standard.

Cash and Investments in Marketable Securities

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Cash and Investments in Marketable Securities

Note 2 — Cash and Investments in Marketable Securities

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

	Estimated Fair Value at
	December 31, 2017		December 31, 2016
Cash and cash equivalents	$	4,762	$	59,640
Short-term investments		291,370		329,462
Long-term investments		57,088		—
Total cash and investments in marketable securities	$	353,220	$	389,102

We invest in liquid, high quality debt securities. Our investments in debt securities are subject to interest rate risk. To minimize the exposure due to an adverse shift in interest rates, we invest in securities with maturities of two years or less and maintain a weighted average maturity of one year or less. As of December 31, 2017, $57.1 million of our total investments had maturities between one and two years and, as of December 31, 2016, all of our investments had maturities of one year or less.

Gross unrealized gains and losses were not significant at either December 31, 2017 or 2016. During the years ended December 31, 2017, 2016 and 2015, we sold available-for-sale securities totaling $37.5 million, $5.0 million, and $42.5 million, respectively, and realized gains and losses were not significant in any of those periods.

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

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

			Estimated Fair Value at
	Fair Value Hierarchy Level		December 31, 2017		December 31, 2016
Corporate notes and bonds		2	$	216,253	$	156,044
Corporate commercial paper		2		128,096		160,920
Obligations of U.S. government agencies		2		2,977		13,749
Available-for-sale investments				347,326		330,713
Money market funds		1		302		51,104
Certificate of deposit	N/A			1,132		2,930
Cash	N/A			4,460		4,355
Total cash and investments in marketable securities			$	353,220	$	389,102

Level 1 —

Quoted prices in active markets for identical assets or liabilities.

Level 2 —

Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices for identical or similar assets or liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.

Level 3 —

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

During the years ended December 31, 2017, 2016 and 2015 there were no transfers between Level 1 and Level 2 of the fair value hierarchy.

At December 31, 2017 and 2016, we had letter of credit arrangements in favor of a landlord and certain vendors totaling $1.1 million and $2.4 million, respectively. These letters of credit are secured by investments of similar amounts.

- Definition

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

+ References + Details

Inventory

12 Months Ended

Dec. 31, 2017

Inventory Disclosure [Abstract]

Inventory

Note 3 — Inventory

Inventory consists of the following (in thousands):

	December 31,
	2017		2016
Raw materials	$	1,796	$	2,055
Work-in-process		4,843		7,311
Finished goods		4,087		1,743
Total inventory	$	10,726	$	11,109

Property, Plant and Equipment

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Property, Plant and Equipment

Note 4 — Property, Plant and Equipment

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

	December 31,
	2017			2016
Building and leasehold improvements	$	81,444		$	75,137
Laboratory equipment		31,214			27,424
Furniture, fixtures and other equipment		27,800			26,590
Manufacturing equipment		20,695			44,237
Depreciable property, plant and equipment at cost		161,153			173,388
Less: accumulated depreciation and amortization		(115,090	)		(111,243	)
Depreciable property, plant and equipment, net		46,063			62,145
Construction-in-progress		1,400			3,456
Property, plant and equipment, net	$	47,463		$	65,601

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

Depreciation and amortization expenses on property, plant and equipment, including depreciation of assets acquired through capital leases, for the years ended December 31, 2017, 2016, and 2015 was $12.6 million, $13.2 million, and $11.4 million, respectively.

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

Senior Secured Notes	12 Months Ended
Senior Secured Notes	Dec. 31, 2017
Debt Disclosure [Abstract]
Senior Secured Notes	Note 5 — Senior Secured Notes On October 5, 2015, we completed the sale and issuance of $250.0 million in aggregate principal amount of 7.75% senior secured notes due 2020 (the “Notes”). The Notes are secured by a first-priority lien on substantially all of our assets and bear interest at a rate of 7.75% per annum payable in cash quarterly in arrears on January 15, April 15, July 15, and October 15 of each year. Interest is calculated based on actual days outstanding over a 360 day year. The Notes will mature on October 5, 2020, at which time the outstanding principal will be due and payable. In connection with the issuance of the Notes, we paid fees and expenses of $8.9 million, of which $8.7 million of transaction and facility fees paid directly to the purchasers of the Notes and other direct issuance costs were capitalized as a debt discount and issuance costs and are recorded as a reduction to the senior secured notes, net liability balance in our Consolidated Balance Sheet. The unamortized balance of these costs is $4.8 million at December 31, 2017 and will be amortized to interest expense over the remainder of the five year term of the Notes. On October 5, 2015, we used a portion of the proceeds from the Notes to redeem the $125.0 million in aggregate principal amount of 12.0% senior secured notes due in 2017 (12% Notes). In addition, on October 5, 2015, we paid $3.3 million of accrued interest on the 12% Notes and made a $12.5 million redemption payment, which includes $1.2 million of additional interest paid to the note holders at redemption. As a result, we received $100.3 million in net proceeds in connection with these transactions. In addition, as a result of these transactions, in the year ended December 31, 2015, we recognized a $14.1 million loss on extinguishment of our 12% Notes, which consists of the $11.3 million redemption premium and $1.2 million of incremental interest paid to the note holders and the write-off of $1.6 million of unamortized issuance costs. 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. The Notes agreement provides that, beginning on October 5, 2017, we may redeem some or all of the Notes, subject to certain prepayment premiums and conditions. 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, 2017, based on a discounted cash flow analysis using Level 3 inputs including financial discount rates, we believe the $250.0 million in principal amount of the Notes is consistent with its fair value.

Leases

12 Months Ended

Dec. 31, 2017

Leases [Abstract]

Leases

Note 6 — Leases

Operating Leases

In August 2017, we entered into a Lease Agreement (the “Lease”) with ARE-San Francisco No. 19, LLC (ARE) and terminated our sublease with Pfizer, Inc., effectively extending our lease term from 2020 to 2030 for our 129,732 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 Lease commenced on September 1, 2017, and will expire January 31, 2030, subject to our right to extend the term of the Lease for two consecutive five-year periods. The monthly base rent for the Mission Bay Facility will escalate over the term of the Lease at various intervals. During the term of the Lease, we are responsible for paying our share of operating expenses specified in the Lease, including insurance costs and taxes. The Lease also obligates Nektar to rent from ARE a total of an additional approximately 23,000 square feet of space at the Mission Bay Facility at specified delivery dates. The Lease includes various covenants, indemnities, defaults, termination rights, security deposits and other provisions customary for lease transactions of this nature. In addition to the Lease, we have entered into other operating leases for locations in San Francisco and India.

We recognize rent expense on a straight-line basis over the lease period. For the year ended December 31, 2017, rent expense was approximately $4.7 million and for the years ended December 31, 2016, and 2015, rent expense was approximately $3.2 million in each year. As of December 31, 2017 and 2016, we had total deferred rent balances of $6.0 million and $6.6 million, respectively, which are recorded in other current and other long-term liabilities in our Consolidated Balance Sheets.

Our future minimum lease payments for our operating leases at December 31, 2017 are as follows (in thousands):

Year ending December 31,
2018	$	5,965
2019		5,511
2020		5,884
2021		8,739
2022		9,024
2023 and thereafter		71,127
Total future minimum lease payments	$	106,250

Capital Leases

During the year ended December 31, 2017, we repaid the $5.1 million due under our capital leases on our Consolidated Balance Sheet as of December 31, 2016 and have no capital lease balances as of December 31, 2017.

Liability Related to the Sale of Future Royalties

12 Months Ended

Dec. 31, 2017

Note 7 — Liability Related to the Sale of Future Royalties

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

The following table shows the activity within the liability account during the year ended December 31, 2017 and for the period from the inception of the royalty transaction on February 24, 2012 (inception) to December 31, 2017 (in thousands):

	Year ended December 31, 2017			Period from inception to December 31, 2017
Liability related to the sale of future royalties—beginning balance	$	108,584		$	—
Proceeds from sale of future royalties		—			124,000
Payments from Nektar to RPI		—			(10,000	)
Non-cash CIMZIA^® and MIRCERA^® royalty revenue		(30,531	)		(137,531	)
Non-cash interest expense recognized		18,869			120,453
Liability related to the sale of future royalties – ending balance		96,922			96,922
Less: unamortized transaction costs		(2,267	)		(2,267	)
Liability related to the sale of future royalties, net	$	94,655		$	94,655

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, 2017, 2016 and 2015, we recognized $30.5 million, $30.2 million, and $22.1 million, respectively, in non-cash royalties from net sales of CIMZIA^® and MIRCERA^®, and we recorded $18.9 million, $19.7 million and $20.6 million, respectively, of related non-cash interest expense.

As royalties are remitted to RPI from Roche and UCB, the balance of the Royalty Obligation will be effectively repaid over the life of the agreement. In order to determine the amortization of the Royalty Obligation, we are required to estimate the total amount of future royalty payments to be received by RPI. The sum of these amounts less the $124.0 million proceeds we received will be recorded as interest expense over the life of the Royalty Obligation. From inception until 2017, our estimate of this total interest expense resulted in an effective annual interest rate of approximately 17%. We periodically assess the estimated royalty payments to RPI from UCB and Roche and to the extent the amount or timing of such payments is materially different than our original estimates, we will prospectively adjust the amortization of the Royalty Obligation. During the three month period ended December 31, 2017, as a result of increases in the forecasted sales of CIMZIA^®, our estimate of the effective annual interest rate over the life of the agreement increased to 17.6%, which results in a prospective interest rate of 21%.

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

In addition, the Purchase and Sale Agreement grants RPI the right to receive certain reports and other information relating to the Royalty Entitlement and contains other representations and warranties, covenants and indemnification obligations that are customary for a transaction of this nature. To our knowledge, we are currently in compliance with these provisions of the Purchase and Sale Agreement; however, if we were to breach our obligations, we could be required to pay damages to RPI that are not limited to the purchase price we received in the sale transaction.

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2017
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 8 — Commitments and Contingencies Purchase Commitments In the normal course of business, we enter into various firm purchase commitments related to contract manufacturing, clinical development and certain other items. As of December 31, 2017, these commitments were approximately $16.5 million, all of which are expected to be paid in 2018. Legal Matters From time to time, we are involved in lawsuits, arbitrations, claims, investigations and proceedings, consisting of intellectual property, commercial, employment and other matters, which arise in the ordinary course of business. We make provisions for liabilities when it is both probable that a liability has been incurred and the amount of the loss can be reasonably estimated. Such provisions are reviewed at least quarterly and adjusted to reflect the impact of settlement negotiations, judicial and administrative rulings, advice of legal counsel, and other information and events pertaining to a particular case. Litigation is inherently unpredictable. If any unfavorable ruling were to occur in any specific period, there exists the possibility of a material adverse impact on the results of our operations of that period and on our cash flows and liquidity. On August 14, 2015, Enzon, Inc. filed a breach of contract complaint in the Supreme Court of the State of New York (Court) claiming damages of $1.5 million (plus interest) for unpaid licensing fees (the “Enzon Litigation”) through the date of the complaint. Enzon alleged that we failed to pay a post-patent expiration immunity fee related to one of the licenses. On June 26, 2017, we entered into a Second Amendment to the Cross-License and Option Agreement (Cross-License Agreement) with Enzon in which we agreed to pay Enzon a sum of $7.0 million to satisfy all past and future obligations of royalty payments pursuant to the Cross-License Agreement and to have the Enzon Litigation dismissed. The Enzon Litigation was dismissed with prejudice on June 30, 2017. We paid $3.5 million in June 2017 and the remaining $3.5 million in December 2017. Of the total $7.0 million consideration, $1.4 million represents our accrued royalty liability to Enzon related to commercial sales of certain products from January 2017 through June 2017 recorded in cost of goods sold for year ended December 31, 2017. In addition, $2.3 million was recorded as a prepaid royalty asset for estimated future commercial sales of certain products through the term of the applicable underlying Enzon patents expiring in March 2018, which Nektar will amortize over this period. As of December 31, 2017, the unamortized prepaid royalty balance is $0.6 million and is included in other current assets. We recorded the remaining $3.3 million of consideration in general and administrative expense in the year ended December 31, 2017. No liability was recorded for this matter on our Consolidated Balance Sheets as of December 31, 2016. Royalty Expense After the termination of our royalty obligations under the Enzon agreement discussed above, we will have no third party licenses that require us to pay royalties based on our sales of certain products and/or on our recognition of royalty revenue under certain of our collaboration agreements. Royalty expense, which is reflected in cost of goods sold in our Consolidated Statements of Operations, was approximately $3.1 million, $3.7 million, and $2.8 million for the years ended December 31, 2017, 2016, and 2015, respectively. 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, the overall maximum amount of any such obligations cannot be reasonably estimated. No liabilities have been recorded for these obligations on our Consolidated Balance Sheets as of December 31, 2017 or 2016. Indemnifications in Connection with Commercial Agreements As part of our collaboration agreements with our partners related to the license, development, manufacture and supply of drugs based on our proprietary technologies and drug candidates, we generally agree to defend, indemnify and hold harmless our partners from and against third party liabilities arising out of the agreement, including product liability (with respect to our activities) and infringement of intellectual property to the extent the intellectual property is developed by us and licensed to our partners. As part of the sale of our royalty interest in the CIMZIA^® and MIRCERA^® products, we and RPI made representations and warranties and entered into certain covenants and ancillary agreements which are supported by indemnity obligations. Additionally, as part of our pulmonary asset sale to Novartis in 2008, we and Novartis made representations and warranties and entered into certain covenants and ancillary agreements which are supported by an indemnity obligation. In the event it is determined that we breached certain of the representations and warranties or covenants and agreements made by us in any such agreements, we could incur substantial indemnification liabilities depending on the timing, nature, and amount of any such claims. Indemnification of Underwriters and Initial Purchasers of our Securities In connection with our sale of equity and senior secured debt securities, we have agreed to defend, indemnify and hold harmless our underwriters or initial purchasers, as applicable, as well as certain related parties from and against certain liabilities, including liabilities under the Securities Act of 1933, as amended. Director and Officer Indemnifications As permitted under Delaware law, and as set forth in our Certificate of Incorporation and our Bylaws, we indemnify our directors, executive officers, other officers, employees, and other agents for certain events or occurrences that may arise while in such capacity. The maximum potential amount of future payments we could be required to make under this indemnification is unlimited; however, we have insurance policies that may limit our exposure and may enable us to recover a portion of any future amounts paid. Assuming the applicability of coverage, the willingness of the insurer to assume coverage, and subject to certain retention, loss limits and other policy provisions, we believe any obligations under this indemnification would not be material, other than an initial $1.8 million per incident for merger and acquisition related claims, $1.8 million per incident for securities related claims and $0.5 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

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Stockholders' Equity

Note 9 — Stockholders’ Equity

Preferred Stock

We have authorized 10,000,000 shares of Preferred Stock with each share having a par value of $0.0001. As of December 31, 2017 and 2016, no preferred shares are designated, issued or outstanding.

Common Stock

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

Equity Compensation Plans

At December 31, 2017, we had 26,761,122 reserved shares of common stock, all of which are reserved for issuance under our equity compensation plans as summarized in the following table (share numbers in thousands):

Plan Category	Number of Securities to be Issued Upon Exercise of Outstanding Options & Vesting of RSUs (a)		Weighted- Average Exercise Price of Outstanding Options (b)		Number of Securities Remaining Available for Issuance Under Equity Compensation Plans (Excluding Securities Reflected in Column(a) (c)
Equity compensation plans approved by security holders(1)		20,999	$	20.55		5,360
Equity compensation plans not approved by security holders		402	$	11.01		—
Total		21,401	$	20.35		5,360

(1)	Includes shares of common stock available for future issuance under our ESPP as of December 31, 2017.

2017 Performance Incentive Plan

Our 2017 Performance Incentive Plan (2017 Plan) was adopted by the Company’s 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. 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 sentence 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 the Company to pay the exercise price of an award granted under the 2017 Plan, as well as any shares exchanged or withheld to satisfy the tax withholding obligations related to any award, will not be available for subsequent awards under the 2017 Plan.

The purpose of the 2017 Plan and our other incentive plans is to promote the success of the Company 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 the Company’s common stock, as well as cash bonus awards. Members of the Board of Directors, officers or employees, certain consultants and advisors of the Company and its subsidiaries are eligible to receive awards under the 2017 Plan. Pursuant to the 2017 Plan, we granted or issued non-qualified stock options and RSUs to employees, officers, and non-employee directors during 2017. 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 the Company’s 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 $4,000 per participant. For the years ended December 31, 2017, 2016, and 2015, we recognized $1.6 million, $1.1 million, and $0.9 million, respectively, of compensation expense in connection with our 401(k) retirement plan.

Change in Control Severance Plan

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

Under the CIC Plan, in the event of a change of control of Nektar and a subsequent termination of employment initiated by us or a successor company other than for Cause (as defined in the CIC Plan) or initiated by the employee for a Good Reason Resignation (as defined in the CIC Plan) in each case within twelve months following a change of control transaction, (i) the Chief Executive Officer would be entitled to receive cash severance pay equal to 24 months base salary plus annual target incentive pay, the extension of employee benefits over this severance period and the full acceleration of unvested outstanding equity awards, and (ii) our Senior Vice Presidents and Vice Presidents (including Principal Fellows) would each be entitled to receive cash severance pay equal to twelve months base salary plus annual target incentive pay, the extension of employee benefits over this severance period and the full acceleration of unvested outstanding equity awards. In the event of a change of control of Nektar and a subsequent termination of employment initiated by the Company or a successor company other than for Cause within twelve months following a change of control transaction, all other employees would each be entitled to receive cash severance pay equal to 6 months base salary plus a pro-rata portion of annual target incentive pay, the extension of employee benefits over this severance period and the full acceleration of each such employee’s unvested outstanding equity awards. Under the CIC Plan, as amended, non-employee directors would also be entitled to full acceleration of vesting of all outstanding stock awards in the event of a change of control transaction.

License and Collaboration Agreements

12 Months Ended

Dec. 31, 2017

Organization Consolidation And Presentation Of Financial Statements [Abstract]

License and Collaboration Agreements

Note 10 — License and Collaboration Agreements

We have entered into various collaboration agreements including license agreements and collaborative research, development and commercialization agreements with various pharmaceutical and biotechnology companies. Under these collaboration arrangements, we are entitled to receive license fees, upfront payments, milestone and other contingent payments, royalties, sales milestone payments, and payments for the manufacture and supply of our proprietary PEGylation materials and/or for research and development activities. All of our collaboration agreements are generally cancelable by our partners without significant financial penalty. Our costs of performing these services are generally included in research and development expense, except that costs for product sales to our collaboration partners are included in cost of goods sold.

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

		Year Ended December 31,
Partner	Agreement	2017		2016		2015
Eli Lilly and Company	NKTR-358	$	130,087	$	—	$	—
Ophthotech Corporation⁽¹⁾	Fovista^®		19,123		1,408		1,398
Bayer Healthcare LLC⁽¹⁾	BAY41-6551 (Amikacin Inhale)		17,931		1,429		1,919
Baxalta Incorporated / Shire	ADYNOVATE^®		11,443		650		10,694
MAP Pharmaceuticals, Inc. / Allergan	SEMPRANA^®		11,000		—		—
Amgen, Inc.	Neulasta^®		5,000		5,000		5,000
AstraZeneca AB	MOVANTIK^®and MOVANTIK^® fixed-dose combination program		4,600		33,000		130,000
Daiichi Sankyo Europe GmbH⁽¹⁾	ONZEALD^TM (NKTR-102)		3,811		3,690		—
Roche⁽¹⁾	PEGASYS^® and MIRCERA^®		—		7,685		12,816
Other			7,970		7,520		3,777
License, collaboration and other revenue		$	210,965	$	60,382	$	165,604

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

As of December 31, 2017, our collaboration agreements with partners included potential future payments for development milestones totaling approximately $305.5 million, including amounts from our agreements with Lilly and Baxalta 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.

Eli Lilly and Company (Lilly): NKTR-358

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

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

We identified our license grant to Lilly, our ongoing Phase 1 clinical development obligation, our drug product development obligation and our obligation to supply clinical trial materials as the significant, non-contingent deliverables under the agreement and concluded that each of these deliverables represents a separate unit of accounting. The valuation of each unit of accounting 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 best estimate of 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 best estimate of selling prices for Phase 1 clinical development, drug product development and clinical supply deliverables based on the nature of the services to be performed and estimates of the associated efforts and third-party rates for similar services.

Based on these estimates at agreement inception, the $150.0 million upfront payment was allocated $125.9 million to the license, $17.6 million to the Phase 1 clinical development and $6.5 million to the drug product development based on our estimate of their relative selling prices. We did not allocate any of the upfront arrangement consideration to the clinical trial material supply obligations as we will receive incremental consideration when we deliver such materials. We recognized license revenue upon the effective date of the arrangement in August 2017. We will recognize revenue related to Phase 1 clinical development and drug product development activities using the proportionate performance method as services are provided over the estimated service period, which we estimate will continue until the end of 2019. As a result, during the year ended December 31, 2017, we recognized $125.9 million of revenue related to the license and $4.2 million of revenue related to Phase 1 clinical development and drug product development activities. We recorded the remaining $19.9 million related to Phase 1 clinical development and drug product development activities as deferred revenue as of December 31, 2017.

Ophthotech Corporation: Fovista^®

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

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

Bayer Healthcare LLC: BAY41-6551 (Amikacin Inhale)

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

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

Baxalta Incorporated: Hemophilia

We are a party to an exclusive research, development, license and manufacturing and supply agreement with Baxalta Incorporated (Baxalta), a subsidiary of Shire plc, 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 Baxalta with its requirements of our proprietary materials. Baxalta is responsible for all clinical development, regulatory, and commercialization expenses. The agreement is terminable by the parties under customary conditions.

This Hemophilia A program includes ADYNOVATE^®, which was approved by the FDA in November 2015 for use in adults and adolescents, aged 12 years and older, who have Hemophilia A, and is now marketed in the U.S. As a result of the FDA’s approval, we earned a $10.0 million development milestone in November 2015. Under the terms of this agreement, we are also entitled to a $10.0 million development milestone due upon marketing authorization in the EU, which was achieved in January 2018. In addition, we are entitled to sales milestones upon achievement of annual sales targets 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 determined that this right to sublicense agreement should be considered a material modification of the existing arrangement described above. We have identified our grant of the right to sublicense and our ongoing obligation to supply PEGylation materials specified in the 2005 agreement as the undelivered units of accounting in the arrangement. We made our best estimates of the selling price of these deliverable and recognized the $11.0 million allocated to the right to sublicense and allocated $1.0 million to our ongoing supply obligation unit of accounting. As of December 31, 2017, we have deferred revenue of approximately $1.0 million related to this agreement, which we expect to recognize through January 2028, the estimated end of our supply obligations under the arrangement.

MAP Pharmaceuticals, Inc.: SEMPRANA^®

In August 2006, we entered into a restated and amended license agreement with MAP Pharmaceuticals, Inc. (MAP) under which we granted a license to technology used by MAP in the development of its drug candidate SEMPRANA^®, a potential treatment for chronic migraine headache. Under our agreement, we are entitled to development milestone payments, royalties and a share of sublicensing payments received by MAP. In January 2011, MAP announced a collaboration with Allergan, Inc. (Allergan) to co-promote SEMPRANA^®, under which MAP has received upfront and sublicensing payments totaling $80.0 million from Allergan. In 2013, Allergan acquired MAP and MAP became a wholly-owned subsidiary of Allergan.

In January 2015, we filed a breach of contract action against Allergan and MAP. In December 2017, we, Allergan and MAP entered into a Settlement Agreement and Release. Pursuant to this agreement, Allergan paid Nektar $15.0 million in December 2017 in exchange for relief of any claims related to our share of payments received by MAP from Allergan as well as a specified development milestone payment due to Nektar. We have no continuing performance obligations under the MAP agreement. As a result, in the year ended December 31, 2017, we recognized $11.0 million as license revenue related to our share of payments due to us under the MAP agreement and recorded the remaining $4.0 million, which primarily represents the reimbursement of legal expenses, as a gain on settlement recorded in general and administrative expenses. As of December 31, 2017, we have no deferred revenue related to this agreement.

Amgen, Inc.: Neulasta^®

In October 2010, we amended and restated an existing supply and license agreement by entering into a supply, dedicated suite and manufacturing guarantee agreement (the amended and restated agreement) and a license agreement with Amgen Inc. and Amgen Manufacturing, Limited (together referred to as Amgen). Under the terms of the amended and restated agreement, we guarantee the manufacture and supply of our proprietary PEGylation materials (Polymer Materials) to Amgen in an existing manufacturing suite to be used exclusively for the manufacture of Polymer Materials for Amgen (the Manufacturing Suite) in our manufacturing facility in Huntsville, Alabama (the Facility). This supply arrangement is on a non-exclusive basis (other than the use of the Manufacturing Suite and certain equipment) whereby we are free to manufacture and supply the Polymer Materials to any other third party and Amgen is free to procure the Polymer Materials from any other third party. Under the terms of the amended and restated agreement, we received a $50.0 million payment in the fourth quarter of 2010 in return for our guaranteeing the supply of certain quantities of Polymer Materials to Amgen including without limitation the Additional Rights described below and manufacturing fees that are calculated based on fixed and variable components applicable to the Polymer Materials ordered by Amgen and delivered by us. Amgen has no minimum purchase commitments. If quantities of the Polymer Materials ordered by Amgen exceed specified quantities, significant additional payments become payable to us in return for our guaranteeing the supply of additional quantities of the Polymer Materials.

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

As of December 31, 2017, we have deferred revenue of approximately $14.2 million related to this agreement, which we expect to recognize through October 2020, the estimated end of our obligations under this agreement.

AstraZeneca AB: MOVANTIK^® (naloxegol oxalate), previously referred to as naloxegol and NKTR-118, and MOVANTIK^® fixed-dose combination program, previously referred to as NKTR-119

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^® and MOVANTIK^® fixed-dose combination program. AstraZeneca is responsible for all research, development and commercialization and is responsible for all drug development and commercialization decisions for MOVANTIK^® and the MOVANTIK^® fixed-dose combination program. AstraZeneca paid us an upfront payment of $125.0 million, which we received in the fourth quarter of 2009 and which was fully recognized as of December 31, 2010. In addition, we have received the payments described further below based on development events related to MOVANTIK^® completed solely by AstraZeneca. We are entitled to receive up to $75.0 million of commercial launch contingent payments related to the MOVANTIK^® fixed-dose combination program, based on development events to be pursued and completed solely by AstraZeneca. In addition, we are entitled to significant and escalating double-digit royalty payments and sales milestone payments based on annual worldwide net sales of MOVANTIK^® and MOVANTIK^® fixed-dose combination products.

On September 16, 2014, the United States Food and Drug Administration (FDA) approved MOVANTIK^® for the treatment of opioid-induced constipation (OIC) in adult patients with chronic, non-cancer pain. On December 9, 2014, AstraZeneca announced that MOVENTIG^® (the naloxegol brand name in the European Union or EU) had been granted Marketing Authorisation by the European Commission (EC) for the treatment of opioid-induced constipation (OIC) in adult patients who have had an inadequate response to laxative(s). In March 2015, we received and recognized a $100.0 million non-refundable payment resulting from the U.S. commercial launch of MOVANTIK^®. In March 2015, we agreed to pay AstraZeneca a total of $10.0 million to fund U.S. television advertising in consideration for certain additional commercial information rights. We recorded this $10.0 million obligation as a liability and made the initial $5.0 million payment to AstraZeneca in July 2015 and the remaining $5.0 million payment in July 2016. We determined that this $10.0 million obligation should be recorded as a reduction of revenue, which we recorded in 2015. In August 2015, we received and recognized as revenue an additional $40.0 million non-refundable payment triggered by the first commercial sale of MOVENTIG^® in Germany.

On March 1, 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 the terms of AstraZeneca’s agreement with Kirin, Kirin made a $70.0 million upfront payment to AstraZeneca and will make additional payments based on achieving market access milestones, tiered net sales royalties, as well as sales milestones. Under our license agreement with AstraZeneca, we will share the upfront payment, market access milestones, royalties and sales milestones from Kirin with AstraZeneca receiving 60% and Nektar receiving 40%. This payment sharing arrangement is in lieu of other royalties payable by AstraZeneca to us and a portion of the sales milestones as described below. Our 40% share of royalty payments made by Kirin to AstraZeneca will be financially equivalent to us receiving high single-digit to low double-digit royalties dependent on the level of Kirin’s net sales. Kirin’s MOVENTIG^® net sales will be included for purposes of achieving the annual global sales milestones payable to us by AstraZeneca and will also be included for purposes of determining the applicable ex-U.S. royalty rate, from the tier schedule in our AstraZeneca license agreement, that will be applied to ex-U.S. sales outside of the Kirin territory. The global sales milestones under our license agreement with AstraZeneca will be reduced in relation to the amount of Kirin MOVENTIG^® net sales that contribute to any given annual sales milestone target. As a result, in April 2016, we received 40% (or $28.0 million) of the $70.0 million payment received by AstraZeneca from Kirin. In the years ended December 31, 2017 and 2016, we recognized a total of $4.6 million and $33.0 million, respectively, related to our share of such license-related payments made to AstraZeneca. As of December 31, 2017, we do not have deferred revenue related to our agreement with AstraZeneca.

Daiichi Sankyo Europe GmbH: ONZEALD^TM (etirinotecan pegol), also referred to as NKTR-102

In December 2017, Daiichi Sankyo Europe GmbH (Daiichi) terminated our collaboration and license agreement made effective in May 2016, under which we granted Daiichi exclusive commercialization rights in the European Economic Area, Switzerland, and Turkey (collectively, the European Territory) to ONZEALD^TM (etirinotecan pegol). Daiichi was responsible for all commercialization activities in the European Territory and we were responsible for supplying Daiichi with ONZEALD^TM and for funding and conducting a Phase 3 confirmatory trial in patients with advanced breast cancer who have brain metastases, which was initiated in the fourth quarter of 2016. Daiichi terminated the agreement after the European Medicines Agency’s Committee for Medicinal Products for Human Use confirmed in November 2017 that it declined the conditional marketing authorization application for ONZEALD^TM in the EU.

Under the terms of the agreement, Daiichi paid us a $20.0 million up-front payment in August 2016, of which $12.5 million was refundable to Daiichi if conditional approval was not achieved and the agreement was terminated. This $12.5 million contingent termination payment from us to Daiichi was recorded in our liability related to refundable upfront payment balance in our Consolidated Balance Sheet at December 31, 2016 and was paid to Daiichi in December 2017.

In 2016, we allocated the $7.5 million non-refundable portion of the $20.0 million upfront payment from Daiichi to the license grant and our development service deliverables based on their relative estimated selling prices. As a result, we recognized $3.7 million of revenue in 2016 from this arrangement, primarily related to the delivery of the license. As a result of the termination of the arrangement, we recognized the remaining $3.2 million of deferred revenue in the three months ended December 31, 2017.

Roche: PEGASYS^® and MIRCERA^®

In February 2012, we entered into a toll-manufacturing agreement with Roche under which we agreed to manufacture the proprietary PEGylation material used by Roche to produce MIRCERA^®. Roche entered into the toll-manufacturing agreement with the objective of establishing us as a secondary back-up supply source on a non-exclusive basis. Under the terms of our toll-manufacturing agreement, Roche paid us a total of $27.0 million, including amounts for the delivery of specified quantities of PEGylation materials, all of which were completed as of January 2013. In addition, in 2013, we delivered additional quantities of PEGylation materials used by Roche to produce PEGASYS^® and MIRCERA^® for total consideration of $18.6 million. As of December 31, 2016, we no longer had any continuing manufacturing or supply obligations under this MIRCERA^®agreement and, therefore, we have no deferred revenue related to this agreement.

In February 1997, we entered into a license, manufacturing and supply agreement with Roche, under which we granted Roche a worldwide, exclusive license to certain intellectual property related to our proprietary PEGylation materials used in the manufacture and commercialization of PEGASYS^®. Our performance obligations under this PEGASYS^® agreement ended on December 31, 2015.

Bristol-Myers Squibb: NKTR-214

On September 21, 2016, we entered into a Clinical Trial Collaboration Agreement (Clinical Trial Agreement) with Bristol-Myers Squibb Company (BMS), pursuant to which we and BMS collaborated to conduct Phase 1/2 clinical trials evaluating our IL-2-based CD122-biased agonist, known as NKTR-214, and BMS’ human monoclonal antibody that binds PD-1, known as Opdivo^® (nivolumab), as a potential combination treatment regimen in five tumor types and eight indications, and such other clinical trials evaluating the combined therapy as may be mutually agreed upon by the parties (each, a Combination Therapy Trial).

We acted as the sponsor of each Combination Therapy Trial. Under the Clinical Trial Agreement, 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 and we have recorded a total of $7.8 million of such reimbursements in the year ended December 31, 2017 and since the inception of our collaboration. Each party was otherwise responsible for its own internal costs, including internal personnel costs, incurred in connection with each Combination Therapy Trial. Nektar and BMS used commercially reasonable efforts to manufacture and supply NKTR-214 and Opdivo^® (nivolumab), respectively, for each Combination Therapy Trial with each party bearing its own costs related thereto.

Ownership of, and global commercial rights to, NKTR-214 remain solely with us under the Clinical Trial Agreement. If we wish to license the right to commercialize NKTR-214 in one of certain major market territories prior to September 30, 2018 (Exclusivity Expiration Date), we must first negotiate with BMS, for a period of three months (Negotiation Period), to grant an exclusive license to develop and commercialize NKTR-214 in any of these major market territories. If we do not reach an agreement with BMS for an exclusive license within the Negotiation Period, we will be free to license any right to NKTR-214 to other parties in any territory worldwide except that in the event that we receive a license offer from a third party during a period of 90 calendar days after the end of the Negotiation Period, we will provide BMS ten business days to match the terms of such third-party offer. After the Exclusivity Expiration Date, we are free to license NKTR-214 without any further obligation to BMS. Each party grants to the other party a non-exclusive, worldwide (subject to certain exceptions in the case of the license granted by BMS), non-transferable and royalty-free research and development license to such licensing party’s patent rights, technology and regulatory documentation to use its compound solely to the extent necessary to discharge its obligations under the Clinical Trial Agreement with respect to the conduct of the Combination Therapy Trials.

The Clinical Trial Agreement will be superseded and replaced by the Strategic Collaboration Agreement entered into between us and BMS on February 13, 2018 (BMS Collaboration Agreement), which is summarized in Note 14, if and when the BMS Collaboration Agreement becomes effective.

Other

In addition, as of December 31, 2017, we have a number of other collaboration agreements, including with our collaboration partners UCB and Halozyme, under which we are entitled to up to a total of $45.5 million of development milestones upon achievement of certain development objectives, as well as sales milestones upon achievement of annual sales targets and royalties based on net sales of commercialized products, if any. However, given the current phase of development of the potential products under these collaboration agreements, we cannot estimate the probability or timing of achieving these milestones. As of December 31, 2017, we have deferred revenue of approximately $2.9 million related to these other collaboration agreements, which we expect to recognize through 2020, the estimated end of our obligations under those agreements.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-Based Compensation

Note 11 — Stock-Based Compensation

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

	Year Ended December 31,
	2017		2016		2015
Cost of goods sold	$	2,333	$	1,620	$	1,142
Research and development		21,252		13,093		9,207
General and administrative		13,030		11,137		9,320
Total stock-based compensation	$	36,615	$	25,850	$	19,669

As of December 31, 2017, total unrecognized compensation costs of $211.8 million related to unvested stock-based compensation arrangements are expected to be recognized as expense over a weighted-average period of 2.1 years.

Black-Scholes Assumptions

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

	Year Ended December 31,
	2017			2016			2015
Average risk-free interest rate		2.0	%		1.4	%		1.6	%
Dividend yield		0.0	%		0.0	%		0.0	%
Average volatility factor		54.2	%		51.7	%		50.8	%
Average weighted average expected life	5.3 years			5.3 years			5.3 years

The average risk-free interest rate is based on the U.S. treasury yield curve in effect at the time of grant for periods commensurate with the expected life of the stock-based award. We have never paid dividends, nor do we expect to pay dividends in the foreseeable future; therefore, we used a dividend yield of 0.0%. 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.

Stock-based compensation expense resulting from our ESPP was not significant in the years ended December 31, 2017, 2016, and 2015.

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, 2016		19,413		$	12.01
Options granted		5,322			40.56
Options exercised		(5,284	)		10.88
Options forfeited & canceled		(625	)		13.69
Outstanding at December 31, 2017		18,826		$	20.35		5.15	$	741,257

Exercisable at December 31, 2017		10,504		$	11.95		3.57	$	501,818

(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, 2017.

The weighted-average grant-date fair value per share of options granted during the years ended December 31, 2017, 2016, and 2015 was $20.08, $6.54, and $6.55, respectively. The total intrinsic value of options exercised during the years ended December 31, 2017, 2016, and 2015 was $84.0 million, $17.9 million, and $20.5 million, respectively. The estimated fair value of options vested during the years ended December 31, 2017, 2016, and 2015 was $19.3 million, $16.7 million, and $16.8 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, 2016		2,248		$	13.53
Granted		1,405			54.14
Vested and released		(875	)		14.05
Forfeited and canceled		(200	)		13.14
Balance at December 31, 2017		2,578		$	35.52	$	153,941

(1)	Aggregate intrinsic value represents the difference between the grant price of the award, which is zero, and the closing market price of our common stock on December 31, 2017.

Income Taxes

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

Note 12 — Income Taxes

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

	Year Ended December 31,
	2017			2016			2015
Domestic	$	(97,938	)	$	(155,375	)	$	(81,931	)
Foreign		1,862			2,727			1,260
Loss before provision for income taxes	$	(96,076	)	$	(152,648	)	$	(80,671	)

Provision for Income Taxes

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

	Year Ended December 31,
	2017		2016			2015
Current:
Federal	$	—	$	—		$	—
State		1		(1	)		(1	)
Foreign		580		992			529
Total Current		581		991			528
Deferred:
Federal		—		—			—
State		—		—			—
Foreign		35		(115	)		(22	)
Total Deferred		35		(115	)		(22	)
Provision for income taxes	$	616	$	876		$	506

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

	Year Ended December 31,
	2017			2016			2015
U.S. federal provision (benefit)
At statutory rate	$	(33,627	)	$	(53,427	)	$	(28,235	)
Tax law changes		248,155			—			—
Non-cash interest expense on liability related to sale of future royalties		6,604			6,899			7,217
Non-deductible officers' compensation		2,547			220			184
Change in valuation allowance		(186,124	)		51,981			22,210
Stock-based compensation		(20,665	)		528			674
Sale of future royalties		(8,236	)		—			—
Research credits		(8,038	)		(4,543	)		(4,529	)
Foreign tax deduction		—			—			1,773
Other		—			(782	)		1,212
Provision for income taxes	$	616		$	876		$	506

Tax Law Changes

The U.S. Tax Cuts and Jobs Act (the Tax Act) was enacted on December 22, 2017. The Tax Act reduces the U.S. federal corporate tax rate from 35% in 2017 to 21% in 2018, requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and creates new taxes on certain foreign sourced earnings. At December 31, 2017, we have not completed our accounting for the tax effects of enactment of the Tax Act; however, in certain cases, as described below, we have made a reasonable estimate of the effects on our existing deferred tax balances and the one-time transition tax.

Deferred Tax Assets and Liabilities

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

	December 31,
	2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	364,864		$	508,406
Research and other credits		94,103			74,917
Stock-based compensation		14,552			26,357
Property, plant and equipment		6,848			6,882
Reserves and accruals		5,659			12,269
Capitalized research expenses		5,497			11,587
Deferred revenue		3,796			23,035
Sale of future royalties		—			1,611
Other		1,156			750
Deferred tax assets before valuation allowance		496,475			665,814
Valuation allowance for deferred tax assets		(496,191	)		(665,514	)
Total deferred tax assets		284			300
Total deferred tax liabilities		—			—
Net deferred tax assets	$	284		$	300

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, the net U.S. deferred tax assets have been fully offset by a valuation allowance. The valuation allowance decreased by $169.3 million during the year ended December 31, 2017 and increased by $52.5 million and $17.3 million during the years ended December 31, 2016 and 2015, respectively. The decrease in the valuation allowance for year ended December 31, 2017 is primarily due to the change in the federal rate. The valuation allowance includes approximately $35.6 million of income tax benefit at both December 31, 2017 and December 31, 2016 related to stock-based compensation that will be included in income tax expense in our Consolidated Statement of Operations when realized.

The one-time transition tax is based on our total post-1986 earnings and profits (E&P) that we previously deferred from U.S. income taxes. As of December 31, 2017, we estimate that there is negative E&P on an aggregate basis and we have not recorded a provisional amount for any one-time transition tax triggered by the Tax Act. We have not yet completed our calculation of the total post-1986 E&P for these foreign subsidiaries. Further, the transition tax is based in part on the amount of those earnings held in cash and other specified assets. This amount may change when we finalize the calculation of post-1986 foreign E&P previously deferred from U.S. federal taxation and finalize the amounts held in cash or other specified assets. 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, 2017, we had a net operating loss carryforward for federal income tax purposes of approximately $1,610.3 million, portions of which will begin to expire in 2018. As of December 31, 2017, we had a total state net operating loss carryforward of approximately $474.0 million, portions of which will begin to expire in 2019. 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 $64.0 million, which will begin to expire in 2019 and state research credits of approximately $33.3 million which have no expiration date. We have federal orphan drug credits of $17.7 million which will begin to expire in 2026. These tax credits are subject to the same limitations discussed above.

Unrecognized tax benefits

We have 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. Any adjustments to 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. The decrease in the unrecognized tax benefits in 2015 primarily relates to a California Supreme Court decision relating to the calculation of apportionment of income.

We file income tax returns in the U.S., California, Alabama, 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 and 2016.

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

	December 31,
	2017			2016		2015
Beginning balance	$	18,413		$	17,384	$	27,522
Tax positions related to current year
Additions:
Federal		1,206			530		529
State		1,666			499		443
Reductions		—			—		—
Tax positions related to prior year
Additions:
Federal		—			—		—
State		—			—		—
Foreign		—			—		—
Reductions		(802	)		—		(11,110	)
Settlements		—			—		—
Lapses in statute of limitations		—			—		—
Ending balance	$	20,483		$	18,413	$	17,384

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, 2017, 2016 and 2015, no significant interest or penalties were recognized relating to unrecognized tax benefits.

Segment Reporting

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Segment Reporting

Note 13 — Segment Reporting

We operate in one business segment which focuses on applying our technology platforms to improve the performance of established drugs and 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 clients in the pharmaceutical and biotechnology industries. Lilly and UCB represented 42% and 12% of our revenue, respectively, for the year ended December 31, 2017. Revenue from AstraZeneca, UCB, Ophthotech and Roche represented 29%, 21%, 19% and 11% of our revenue, respectively, for the year ended December 31, 2016. Revenue from AstraZeneca and UCB represented 57% and 13% of our revenue, respectively, for the year ended December 31, 2015 .

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

	Year Ended December 31,
	2017		2016		2015
United States	$	190,810	$	39,147	$	40,400
Europe		116,901		126,289		190,384
Total revenue	$	307,711	$	165,436	$	230,784

At December 31, 2017, $41.7 million, or approximately 88%, of the net book value of our property, plant and equipment was located in the United States and $5.8 million, or approximately 12%, was located in India. At December 31, 2016, $48.8 million, or approximately 74%, of the net book value of our property, plant and equipment was located in the United States, $10.4 million, or approximately 16% was located at contract manufacturers in Germany and the Netherlands, $5.6 million, or approximately 9%, was located in India, and $0.8 million or approximately 1%, was located in other countries.

Subsequent Event	12 Months Ended
Subsequent Event	Dec. 31, 2017
Subsequent Events [Abstract]
Subsequent Event	Note 14 — Subsequent Event On February 13, 2018, we entered into the BMS Collaboration Agreement with BMS, pursuant to which we and BMS will jointly develop NKTR-214, including, without limitation, in combination with BMS’s Opdivo^® (nivolumab) and Opdivo^® plus Yervoy^® (ipilimumab), and other compounds of BMS, us or any third party. The parties have agreed to jointly commercialize NKTR-214 on a worldwide basis. BMS will pay us a non-refundable upfront cash payment of $1.0 billion. We are eligible to receive additional cash payments of a total of up to $1.43 billion upon achievement of certain development and regulatory milestones and a total of up to $350.0 million upon achievement of certain sales milestones. We will book all worldwide sales and revenue for NKTR-214. We will share global commercialization profits and losses with BMS for NKTR-214, with Nektar sharing 65% and BMS sharing 35% of the net profits and losses. BMS will lead commercialization for combinations of NKTR-214 with BMS proprietary medicines, and we will lead all other commercialization efforts for NKTR-214. We will have the final decision-making authority regarding the pricing for NKTR-214. NKTR-214 will be sold on a stand-alone basis and there will be no fixed-dose combinations or co-packaging without the consent of both parties. Under the BMS Collaboration Agreement, we and BMS will collaborate to develop and conduct clinical studies of NKTR-214 pursuant to a joint development plan, which initially includes a series of registration-enabling trials in more than 20 indications in nine tumor types and may be updated and expanded only upon mutual agreement of the parties. The parties will share the development costs for NKTR-214 in combination regimens based on each party’s relative ownership interest in the compounds included in the regimens. Pursuant to a Share Purchase Agreement entered into by us and BMS on February 13, 2018 (Purchase Agreement), BMS has also agreed to purchase 8,284,600 shares of our common stock for total cash consideration of $850.0 million, or $102.60 per share. The closing of the share purchase is subject to the expiration or early termination of the waiting period (and any extension thereof) under the Hart-Scott-Rodino Antitrust Improvements Act of 1976 and other customary closing conditions. The closings of the BMS Collaboration Agreement and the Purchase Agreement will be simultaneous and are expected to occur during the second quarter of 2018.

Selected Quarterly Financial Data

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Selected Quarterly Financial Data

Note 15 — 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 you should not rely on our results for any one quarter as an indication of our future performance. Certain items previously reported in specific financial statement captions have been reclassified to conform to the current period presentation. Such reclassifications have not materially impacted previously reported total revenues, operating loss or net loss. All data is in thousands except per share information.

	Year Ended December 31, 2017											Year Ended December 31, 2016
	Q1			Q2			Q3		Q4			Q1			Q2			Q3			Q4
Product sales	$	4,756		$	15,693		$	4,448	$	7,791		$	14,099		$	12,867		$	14,698		$	13,690
Total revenue	$	24,728		$	34,589		$	152,928	$	95,466		$	58,882		$	32,768		$	36,336		$	37,450
Cost of goods sold	$	6,131		$	8,989		$	5,674	$	9,753		$	8,870		$	7,708		$	7,033		$	6,604
Research and development expenses	$	61,058		$	60,260		$	65,714	$	81,429		$	49,268		$	52,350		$	51,951		$	50,232
Operating income (loss)	$	(54,437	)	$	(50,656	)	$	69,485	$	(24,034	)	$	(9,484	)	$	(38,325	)	$	(32,901	)	$	(32,145	)
Net income (loss)	$	(63,866	)	$	(59,871	)	$	60,871	$	(33,826	)	$	(19,498	)	$	(48,603	)	$	(43,224	)	$	(42,199	)
Net income (loss) per share(1)
Basic	$	(0.42	)	$	(0.39	)	$	0.39	$	(0.21	)	$	(0.14	)	$	(0.36	)	$	(0.32	)	$	(0.28	)
Diluted	$	(0.42	)	$	(0.39	)	$	0.37	$	(0.21	)	$	(0.14	)	$	(0.36	)	$	(0.32	)	$	(0.28	)

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

Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization	Organization We are a research-based biopharmaceutical company headquartered in San Francisco, California and incorporated in Delaware. We are developing a pipeline of drug candidates that utilize our advanced polymer conjugate technology platforms, which are designed to enable the development of new molecular entities that target known mechanisms of action. Our research and development pipeline of new investigational drugs includes treatments for cancer, autoimmune disease and chronic pain. Our research and development activities have required significant ongoing investment to date and are expected to continue to require significant investment. As a result, we expect to continue to incur substantial losses and negative cash flows from operations in the future. We have financed our operations primarily through cash generated from licensing, collaboration and manufacturing agreements and financing transactions. At December 31, 2017, we had approximately $353.2 million 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	Basis of Presentation, Principles of Consolidation and Use of Estimates Our consolidated financial statements include the financial position, results of operations and cash flows of our wholly-owned subsidiaries: Nektar Therapeutics (India) Private Limited and Nektar Therapeutics UK Limited. All intercompany accounts and transactions have been eliminated in consolidation. Our Consolidated Financial Statements are denominated in U.S. dollars. Accordingly, changes in exchange rates between the applicable foreign currency and the U.S. dollar will affect the translation of each foreign subsidiary’s financial results into U.S. dollars for purposes of reporting our consolidated financial results. Translation gains and losses are included in accumulated other comprehensive income (loss) in the stockholders’ equity section of the Consolidated Balance Sheets. To date, such cumulative translation adjustments have not been significant to our consolidated financial position. Aggregate gross foreign currency transaction gains (losses) recorded in operations for the years ended December 31, 2017, 2016, and 2015 were not significant. The preparation of consolidated financial statements in conformity with U.S. generally accepted accounting principles (GAAP) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Accounting estimates and assumptions are inherently uncertain. Actual results could differ materially from those estimates and assumptions. Our estimates include those related to estimated selling prices of deliverables in collaboration agreements, estimated periods of performance, the net realizable value of inventory, the impairment of investments, the impairment of goodwill and long-lived assets, contingencies, accrued clinical trial expenses, estimated non-cash royalty revenue and non-cash interest expense from our liability related to our sale of future royalties, stock-based compensation, and ongoing litigation, among other estimates. We base our estimates on historical experience and on other assumptions that management believes are reasonable under the circumstances. These estimates form the basis for making judgments about the carrying values of assets and liabilities when these values are not readily apparent from other sources. As appropriate, estimates are assessed each period and updated to reflect current information and any changes in estimates will generally be reflected in the period first identified.
Reclassifications	Reclassifications Certain items previously reported in specific financial statement captions have been reclassified to conform to the current period presentation, including as a result of the adoption of new accounting guidance related to the classification of deferred tax assets described below. Such reclassifications do not materially impact previously reported revenue, operating loss, net loss, total assets, liabilities or stockholders’ equity.
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. 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, are classified as short-term investments. Investments in securities with remaining maturities of over one year are classified 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. Interest and dividends on securities classified as available-for-sale, as well as amortization of premiums and accretion of discounts to maturity, are included in interest income. Realized gains and losses and declines in value of available-for-sale securities judged to be other-than-temporary, if any, are included 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 U.S. government obligations, money market instruments and funds, and corporate bonds 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 located in the U.S. and Europe and with whom we have multi-year arrangements. Our accounts receivable balance contains billed and unbilled trade receivables from product sales, milestones, other contingent payments and royalties, as well as time and materials based billings from collaborative research and development agreements. When appropriate, we provide for an allowance for doubtful accounts by reserving for specifically identified doubtful accounts. We generally do not require collateral from our customers. We perform a regular review of our customers’ credit risk and payment histories, including payments made subsequent to year-end. We have not experienced significant credit losses from our accounts receivable. At December 31, 2017, four different customers represented 43%, 20%, 19% and 14%, respectively, of our accounts receivable. At December 31, 2016, three different customers represented 39%, 32%, and 13%, respectively, of our accounts receivable.
Inventory and Significant Supplier Concentrations	Inventory and Significant Supplier Concentrations Inventory is generally manufactured upon receipt of firm purchase orders from our collaboration partners. Inventory includes direct materials, direct labor, and manufacturing overhead and cost is determined on a first-in, first-out basis. Inventory is valued at the lower of cost or net realizable value and defective or excess inventory is written down to net realizable value based on historical experience or projected usage. Inventory related to our research and development activities is expensed when purchased. We are dependent on our suppliers and contract manufacturers to provide raw materials, drugs and devices of appropriate quality and reliability and to meet applicable contract and regulatory requirements. In certain cases, we rely on single sources of supply of one or more critical materials. Consequently, in the event that supplies are delayed or interrupted for any reason, our ability to develop and produce our drug candidates or our ability to meet our supply obligations could be significantly impaired, which could have a material adverse effect on our business, financial condition and results of operations.
Long-Lived Assets	Long-Lived Assets Property, plant and equipment are stated at cost. Major improvements are capitalized, while maintenance and repairs are expensed when incurred. Manufacturing, laboratory and other equipment are depreciated using the straight-line method generally over estimated useful lives of three to ten years. Buildings are depreciated using the straight-line method generally over the estimated useful life of twenty years. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful life or the remaining term of the lease. Goodwill represents the excess of the price paid for another entity over the fair value of the assets acquired and liabilities assumed in a business combination. We are organized in one reporting unit and evaluate the goodwill for the Company as a whole. Goodwill has an indefinite useful life and is not amortized, but instead tested for impairment at least annually in the fourth quarter of each year using an October 1 measurement date. We assess the impairment of long-lived assets whenever events or changes in business circumstances indicate that the carrying amounts of the assets may not be fully recoverable. When such events occur, we determine whether there has been an impairment in value by comparing the carrying value of the asset with its fair value, as measured by the anticipated undiscounted net cash flows associated with the asset. In the case of goodwill impairment, market capitalization is generally used as the measure of fair value. If an impairment in value exists, the asset is written down to its estimated fair value.
Revenue Recognition	Revenue Recognition Our revenue is derived from our arrangements with pharmaceutical and biotechnology collaboration partners and may result from one or more of the following: upfront and license fees, payments for contract research and development, milestone and other contingent payments, manufacturing and supply payments, and royalties. Our performance obligations under our collaborations may include licensing our intellectual property, manufacturing and supply obligations, and research and development obligations. In order to account for the multiple-element arrangements, we identify the deliverables included within the arrangement and evaluate which deliverables represent separate units of accounting. Analyzing the arrangement to identify deliverables requires the use of judgment, and each deliverable may be an obligation to deliver goods or services, a right or license to use an asset, or another performance obligation. Revenue is recognized separately for each identified unit of accounting when the basic revenue recognition criteria are met: there is persuasive evidence that an arrangement exists, delivery has occurred, the price is fixed or determinable, and collection is reasonably assured. At the inception of each new multiple-element arrangement or the material modification of an existing multiple-element arrangement, we allocate all consideration received under multiple-element arrangements to all units of accounting based on the relative selling price method, generally based on our best estimate of selling price (ESP). The objective of ESP is to determine the price at which we would transact a sale if the product or service was sold on a stand-alone basis. We determine ESP for the elements in our collaboration arrangements by considering multiple factors including, but not limited to, technical complexity of the performance obligation and similarity of elements to those performed under previous arrangements. Since we apply significant judgment in arriving at the ESPs, any material change in our estimates would significantly affect the allocation of the total consideration to the different elements of a multiple element arrangement. Product sales Product sales are primarily derived from fixed price manufacturing and supply agreements with our collaboration partners. Our products are tested for adherence to technical specifications prior to shipment, accordingly, we have not experienced any significant returns from our customers. Royalty revenue Generally, we are entitled to royalties from our collaboration partners based on the net sales of their approved drugs that are marketed and sold in one or more countries where we hold royalty rights. We recognize royalty revenue when the cash is received or when the royalty amount to be received is estimable and collection is reasonably assured. With respect to the non-cash royalties related to our sale of future royalties described in Note 7, revenue is recognized when estimable, otherwise, revenue is recognized during the period in which the related royalty report is received, which generally occurs in the quarter after the applicable product sales are made. License, collaboration and other revenue The amount of upfront fees and other payments received by us in license and collaboration arrangements that are allocated to continuing performance obligations, such as manufacturing and supply obligations, is deferred and generally recognized ratably over our expected performance period under each respective arrangement. We make our best estimate of the period over which we expect to fulfill our performance obligations, which may include technology transfer assistance, research activities, clinical development activities, and manufacturing activities from research and development through the commercialization of the product. Given the uncertainties of these collaboration arrangements, significant judgment is required to determine the duration of the performance period and this estimate is periodically re-evaluated. Upon the termination of each of our license and collaboration arrangements and if no additional services are required to be performed by us, all non-refundable, non-creditable amounts previously deferred from the arrangement are recognized as revenue. Contingent consideration received from the achievement of a substantive milestone is recognized in its entirety in the period in which the milestone is achieved, which we believe is consistent with the substance of our performance under our various license and collaboration agreements. A milestone is defined as an event (i) that can only be achieved based in whole or in part either on the entity’s performance or on the occurrence of a specific outcome resulting from the entity’s performance, (ii) for which there is substantive uncertainty at the date the arrangement is entered into that the event will be achieved, and (iii) that would result in additional payments being due to the entity. A milestone is substantive if the consideration earned from the achievement of the milestone is consistent with our performance required to achieve the milestone or the increase in value to the collaboration resulting from our performance, relates solely to our past performance, and is reasonable relative to all of the other deliverables and payments within the arrangement. Our license and collaboration agreements with our partners provide for payments to us upon the achievement of development milestones, such as the completion of clinical trials or regulatory submissions, approvals by regulatory authorities, and commercial launches of drugs. Given the challenges inherent in developing and obtaining regulatory approval for drug products and in achieving commercial launches, there was substantial uncertainty whether any such milestones would be achieved at the time of execution of these licensing and collaboration agreements. In addition, we evaluated whether the development milestones met the remaining criteria to be considered substantive. As a result of our analysis, we consider our remaining development milestones under all of our license and collaboration agreements to be substantive and, accordingly, we recognize as revenue payments received from each milestone only if and as such milestone is achieved. Our license and collaboration agreements with certain partners also provide for contingent payments to us based solely upon the performance of the respective partner. For such contingent amounts, we recognize the payments as revenue when earned under the applicable contract, which is generally upon completion of performance by the respective partner, provided that collection is reasonably assured. Our license and collaboration agreements with our partners also provide for payments to us upon the achievement of specified sales volumes of approved drugs. We consider these payments to be similar to royalty payments and we recognize such sales-based payments upon achievement of such sales volumes, provided that collection is reasonably assured.
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 Bristol-Myers Squibb, 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 accruals for the estimated costs of our clinical trial activities performed by third parties. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows to our vendors. Payments under the contracts depend on factors such as the achievement of certain events, successful enrollment of patients, and completion of certain clinical trial activities. We generally accrue costs associated with the start-up and reporting phases of the clinical trials ratably over the estimated duration of the start-up and reporting phases. We generally accrue costs associated with the treatment phase of clinical trials based on the total estimated cost of the treatment phase on a per patient basis and we expense the per patient cost ratably over the estimated patient treatment period based on patient enrollment in the trials. In specific circumstances, such as for certain time-based costs, we recognize clinical trial expenses using a methodology that we consider to be more reflective of the timing of costs incurred. Advance payments for goods or services that will be used or rendered for future research and development activities are capitalized as prepaid expenses and recognized as expense as the related goods are delivered or the related services are performed. We base our estimates on the best information available at the time. However, additional information may become available to us which may allow us to make a more accurate estimate in future periods. In this event, we may be required to record adjustments to research and development expenses in future periods when the actual level of activity becomes more certain. Such increases or decreases in cost are generally considered to be changes in estimates and will be reflected in research and development expenses in the period identified.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation arrangements include stock option grants and restricted stock unit (RSU) awards under our equity incentive plans, as well as shares issued under our Employee Stock Purchase Plan (ESPP), through which employees may purchase our common stock at a discount to the market price. We use the Black-Scholes option pricing model for the respective grant to determine the estimated fair value of the option on the date of grant (grant date fair value) and the estimated fair value of common stock purchased under the ESPP. The Black-Scholes option pricing model requires the input of highly subjective assumptions. These variables include, but are not limited to, our stock price volatility over the term of the awards, and actual and projected employee stock option exercise behaviors. Because our employee stock options have characteristics significantly different from those of traded options, and because changes in the subjective input assumptions can materially affect the fair value estimate, in management’s opinion, the existing models may not provide a reliable single measure of the fair value of our employee stock options or common stock purchased under the ESPP. The fair value of an RSU is equal to the closing price of our common stock on the grant date. Management will continue to assess the assumptions and methodologies used to calculate the estimated fair value of stock-based compensation. Circumstances may change and additional data may become available over time, which could result in changes to these assumptions and methodologies, and which could materially impact our fair value determination. We expense the value of the portion of the option or award on a straight line basis over the requisite service periods in our Consolidated Statements of Operations and recognize forfeitures of options and awards as they occur. For options and awards that vest upon the achievement of performance milestones, we estimate the vesting period based on our evaluation of the probability of achievement of each respective milestone and the related estimated date of achievement. Stock-based compensation expense for purchases under the ESPP is recognized over the respective six-month purchase period. Expense amounts are recorded in cost of goods sold, research and development expense, and general and administrative expense based on the function of the applicable employee. Stock-based compensation charges are non-cash charges and as such have no impact on our reported cash flows.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated based on the weighted-average number of common shares outstanding during the periods presented. For all periods presented in the Consolidated Statements of Operations, 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 anti-dilutive effect on net loss per share. During 2017, 2016 and 2015, potentially dilutive securities consisted of common shares underlying outstanding stock options and RSUs. There were weighted average outstanding stock options and RSUs of 20.6 million, 19.9 million and 21.1 million during the years ended December 31, 2017, 2016 and 2015, respectively.
Income Taxes	Income Taxes We account for income taxes under the liability method. Under this method, deferred tax assets and liabilities are determined based on differences between the financial reporting and tax reporting bases of assets and liabilities and are measured using enacted tax rates and laws that are expected to be in effect when the differences are expected 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 such determination is made. 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 loss	Comprehensive loss Comprehensive 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) is comprised of net loss, gains and losses from the foreign currency translation of the assets and liabilities of our India and UK subsidiaries, and unrealized gains and losses on investments in available-for-sale securities.
Adoption of New Accounting Principle	Adoption of New Accounting Principle In March 2016, the Financial Accounting Standards Board (FASB) issued guidance to simplify several aspects of employee share-based payment accounting, including forfeitures, income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. This guidance was effective for our interim and annual periods beginning January 1, 2017. As a result of the adoption of this guidance, as of January 1, 2017, we recorded a $0.2 million charge to our accumulated deficit in our Consolidated Balance Sheet related to our election to recognize forfeitures of awards as they occur. In addition, prior to adoption of this guidance, tax attributes related to stock option windfall deductions were not recorded until they resulted in a reduction of cash tax payable. As of December 31, 2016, the excluded windfall deductions for federal and state purposes were $20.6 million and $9.8 million, respectively. Upon adoption, we recognized the excluded windfall deductions as a deferred tax asset on a tax-effected basis with a corresponding increase in the valuation allowance. In November 2015, the FASB issued guidance to require that deferred tax assets and liabilities be classified as noncurrent on the balance sheet. Previous guidance required deferred tax assets and liabilities to be separated into current and noncurrent amounts on the balance sheet. Accordingly, as of January 1, 2017, we reclassified $0.3 million from other current assets to our other assets balance. This reclassification was applied retrospectively to these balances in our Consolidated Balance Sheet as of December 31, 2016.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the FASB issued guidance codified in Accounting Standards Codification (ASC) 606, Revenue Recognition — Revenue from Contracts with Customers, which supersedes the guidance in ASC 605, Revenue Recognition, and is effective for public companies for annual and interim periods beginning after December 15, 2017. The FASB has issued numerous updates that provide clarification on a number of specific issues as well as requiring additional disclosures. We plan to adopt the standard in the first quarter of 2018 using the modified retrospective method. The new guidance requires the application of a five-step model to determine the amount and timing of revenue to be recognized and requires that we recognize revenue in a manner that reasonably reflects the delivery of our goods or services to customers in return for expected consideration. To achieve this core principle, the guidance provides the following steps: (1) identify the contract(s) with a customer; (2) identify the performance obligations in the contract; (3) determine the transaction price; (4) allocate the transaction price to the performance obligations in the contract; and (5) recognize revenue when (or as) the entity satisfies a performance obligation. Under ASC 606, companies may need to use more judgment and make more estimates than under ASC 605 in the application of this five-step process. We are continuing to assess the impact of the new guidance on our accounting policies and procedures and are evaluating the new requirements as applied to existing collaboration agreements, both in terms of the cumulative adjustment to opening accumulated deficit and our subsequent recognition of revenue. Since each collaboration agreement is unique, we will separately assess each agreement (see Note 10 for a discussion of our existing collaboration agreements) under the new standard. We anticipate that the adoption of ASC 606 will have the following impact to our revenue recognition for a collaboration agreement: (i) Changes in revenue recognition for distinct licenses of functional intellectual property may result in a timing difference of revenue recognition between the current literature and ASC 606. For certain of our arrangements, the value associated with the licenses and certain other deliverables have been assessed as one unit of accounting and recognized over a period of time in which services are rendered or made available to our customer pursuant to revenue recognition guidance in effect for such arrangements at the time such arrangements commenced. For certain other arrangements, under current ASC 605 guidance, we identified the value of the license as a separate unit of accounting and recognize revenue upon issuance of the license. Under ASC 606, we may continue to recognize revenue for such licenses upon delivery of the license. (ii) For other consideration, including milestone payments or contingent payments from our collaboration partners, under our current accounting policy, we recognize such payments as revenue in the period that the payment-triggering event occurred or is achieved. The new revenue standard, however, may require us to recognize these payments before the payment-triggering event is completely achieved, subject to management’s assessment of whether it is probable that the triggering event will be achieved and that a significant reversal in the amount of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is subsequently resolved. (iii) We will recognize revenue for sales-based royalties and commercial sales-based milestones in the period of the related sale based on estimates, rather than recording them as reported by the customer. We currently estimate that, upon adoption on January 1, 2018, we will record an adjustment to decrease our accumulated deficit by approximately $11.0 million to $13.0 million for amounts that would be recognized as of December 31, 2017 under ASC 606, but are not recognized under the current ASC 605 guidance. This estimated adjustment primarily consists of approximately $11.0 million for the accrual of royalties due to us related to net sales in the three months ended December 31, 2017 that we would have recognized in 2018 under current guidance. The estimated adjustment also includes up to approximately $2.0 million related to the recognition of the unamortized portion of upfront payment amounts under ASC 606 that are required to be deferred as of December 31, 2017 under current guidance. We will finalize our assessments in the first quarter of 2018 as we adopt ASC 606. In February 2016, the FASB issued guidance to amend a number of aspects of lease accounting, including requiring lessees to recognize almost all leases with a term greater than one year as a right-of-use asset and corresponding liability, measured at the present value of the lease payments. The guidance will become effective for us beginning in the first quarter of 2019 and is required to be adopted using a modified retrospective approach. Early adoption is permitted. We are currently evaluating the impact of the adoption of this standard.
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 Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2017

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, 2017		December 31, 2016
Cash and cash equivalents	$	4,762	$	59,640
Short-term investments		291,370		329,462
Long-term investments		57,088		—
Total cash and investments in marketable securities	$	353,220	$	389,102

Portfolio of Cash and Investments in Marketable Securities

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

			Estimated Fair Value at
	Fair Value Hierarchy Level		December 31, 2017		December 31, 2016
Corporate notes and bonds		2	$	216,253	$	156,044
Corporate commercial paper		2		128,096		160,920
Obligations of U.S. government agencies		2		2,977		13,749
Available-for-sale investments				347,326		330,713
Money market funds		1		302		51,104
Certificate of deposit	N/A			1,132		2,930
Cash	N/A			4,460		4,355
Total cash and investments in marketable securities			$	353,220	$	389,102

Inventory (Tables)

12 Months Ended

Dec. 31, 2017

Inventory Disclosure [Abstract]

Inventory

Inventory consists of the following (in thousands):

	December 31,
	2017		2016
Raw materials	$	1,796	$	2,055
Work-in-process		4,843		7,311
Finished goods		4,087		1,743
Total inventory	$	10,726	$	11,109

Property, Plant and Equipment (Tables)

12 Months Ended

Dec. 31, 2017

Property Plant And Equipment [Abstract]

Property, Plant and Equipment

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

	December 31,
	2017			2016
Building and leasehold improvements	$	81,444		$	75,137
Laboratory equipment		31,214			27,424
Furniture, fixtures and other equipment		27,800			26,590
Manufacturing equipment		20,695			44,237
Depreciable property, plant and equipment at cost		161,153			173,388
Less: accumulated depreciation and amortization		(115,090	)		(111,243	)
Depreciable property, plant and equipment, net		46,063			62,145
Construction-in-progress		1,400			3,456
Property, plant and equipment, net	$	47,463		$	65,601

Leases (Tables)

12 Months Ended

Dec. 31, 2017

Leases [Abstract]

Future Minimum Lease Payments for Operating Leases

Our future minimum lease payments for our operating leases at December 31, 2017 are as follows (in thousands):

Year ending December 31,
2018	$	5,965
2019		5,511
2020		5,884
2021		8,739
2022		9,024
2023 and thereafter		71,127
Total future minimum lease payments	$	106,250

Liability Related to the Sale of Future Royalties (Tables)

12 Months Ended

Dec. 31, 2017

Summary of Liability Related to Potential Future Royalties

	Year ended December 31, 2017			Period from inception to December 31, 2017
Liability related to the sale of future royalties—beginning balance	$	108,584		$	—
Proceeds from sale of future royalties		—			124,000
Payments from Nektar to RPI		—			(10,000	)
Non-cash CIMZIA^® and MIRCERA^® royalty revenue		(30,531	)		(137,531	)
Non-cash interest expense recognized		18,869			120,453
Liability related to the sale of future royalties – ending balance		96,922			96,922
Less: unamortized transaction costs		(2,267	)		(2,267	)
Liability related to the sale of future royalties, net	$	94,655		$	94,655

Stockholders' Equity (Tables)

12 Months Ended

Dec. 31, 2017

Equity [Abstract]

Summarization of Common Stock Shares for Issuance Under Existing Equity Compensation Plans

Plan Category	Number of Securities to be Issued Upon Exercise of Outstanding Options & Vesting of RSUs (a)		Weighted- Average Exercise Price of Outstanding Options (b)		Number of Securities Remaining Available for Issuance Under Equity Compensation Plans (Excluding Securities Reflected in Column(a) (c)
Equity compensation plans approved by security holders(1)		20,999	$	20.55		5,360
Equity compensation plans not approved by security holders		402	$	11.01		—
Total		21,401	$	20.35		5,360

(1)	Includes shares of common stock available for future issuance under our ESPP as of December 31, 2017.

License and Collaboration Agreements (Tables)

12 Months Ended

Dec. 31, 2017

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	2017		2016		2015
Eli Lilly and Company	NKTR-358	$	130,087	$	—	$	—
Ophthotech Corporation⁽¹⁾	Fovista^®		19,123		1,408		1,398
Bayer Healthcare LLC⁽¹⁾	BAY41-6551 (Amikacin Inhale)		17,931		1,429		1,919
Baxalta Incorporated / Shire	ADYNOVATE^®		11,443		650		10,694
MAP Pharmaceuticals, Inc. / Allergan	SEMPRANA^®		11,000		—		—
Amgen, Inc.	Neulasta^®		5,000		5,000		5,000
AstraZeneca AB	MOVANTIK^®and MOVANTIK^® fixed-dose combination program		4,600		33,000		130,000
Daiichi Sankyo Europe GmbH⁽¹⁾	ONZEALD^TM (NKTR-102)		3,811		3,690		—
Roche⁽¹⁾	PEGASYS^® and MIRCERA^®		—		7,685		12,816
Other			7,970		7,520		3,777
License, collaboration and other revenue		$	210,965	$	60,382	$	165,604

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

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Stock-Based Compensation Expense

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

	Year Ended December 31,
	2017		2016		2015
Cost of goods sold	$	2,333	$	1,620	$	1,142
Research and development		21,252		13,093		9,207
General and administrative		13,030		11,137		9,320
Total stock-based compensation	$	36,615	$	25,850	$	19,669

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

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

	Year Ended December 31,
	2017			2016			2015
Average risk-free interest rate		2.0	%		1.4	%		1.6	%
Dividend yield		0.0	%		0.0	%		0.0	%
Average volatility factor		54.2	%		51.7	%		50.8	%
Average weighted average expected life	5.3 years			5.3 years			5.3 years

Stock Option Activity Under Equity Incentive Plans

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

	Number of Shares			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Life (in Years)		Aggregate Intrinsic Value(1)
Outstanding at December 31, 2016		19,413		$	12.01
Options granted		5,322			40.56
Options exercised		(5,284	)		10.88
Options forfeited & canceled		(625	)		13.69
Outstanding at December 31, 2017		18,826		$	20.35		5.15	$	741,257

Exercisable at December 31, 2017		10,504		$	11.95		3.57	$	501,818

(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, 2017.

Restricted Stock Units (RSU) [Member]

Restricted Stock Unit Award Activity

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

	Units Issued			Weighted- Average Grant Date Fair Value		Aggregate Intrinsic Value(1)
Balance at December 31, 2016		2,248		$	13.53
Granted		1,405			54.14
Vested and released		(875	)		14.05
Forfeited and canceled		(200	)		13.14
Balance at December 31, 2017		2,578		$	35.52	$	153,941

(1)	Aggregate intrinsic value represents the difference between the grant price of the award, which is zero, and the closing market price of our common stock on December 31, 2017.

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Loss Before Provision for Income Taxes

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

	Year Ended December 31,
	2017			2016			2015
Domestic	$	(97,938	)	$	(155,375	)	$	(81,931	)
Foreign		1,862			2,727			1,260
Loss before provision for income taxes	$	(96,076	)	$	(152,648	)	$	(80,671	)

Provision for Income Taxes

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

	Year Ended December 31,
	2017		2016			2015
Current:
Federal	$	—	$	—		$	—
State		1		(1	)		(1	)
Foreign		580		992			529
Total Current		581		991			528
Deferred:
Federal		—		—			—
State		—		—			—
Foreign		35		(115	)		(22	)
Total Deferred		35		(115	)		(22	)
Provision for income taxes	$	616	$	876		$	506

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 35% to pretax loss as follows (in thousands):

	Year Ended December 31,
	2017			2016			2015
U.S. federal provision (benefit)
At statutory rate	$	(33,627	)	$	(53,427	)	$	(28,235	)
Tax law changes		248,155			—			—
Non-cash interest expense on liability related to sale of future royalties		6,604			6,899			7,217
Non-deductible officers' compensation		2,547			220			184
Change in valuation allowance		(186,124	)		51,981			22,210
Stock-based compensation		(20,665	)		528			674
Sale of future royalties		(8,236	)		—			—
Research credits		(8,038	)		(4,543	)		(4,529	)
Foreign tax deduction		—			—			1,773
Other		—			(782	)		1,212
Provision for income taxes	$	616		$	876		$	506

Significant Components of Deferred Tax Assets and Liabilities

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

	December 31,
	2017			2016
Deferred tax assets:
Net operating loss carryforwards	$	364,864		$	508,406
Research and other credits		94,103			74,917
Stock-based compensation		14,552			26,357
Property, plant and equipment		6,848			6,882
Reserves and accruals		5,659			12,269
Capitalized research expenses		5,497			11,587
Deferred revenue		3,796			23,035
Sale of future royalties		—			1,611
Other		1,156			750
Deferred tax assets before valuation allowance		496,475			665,814
Valuation allowance for deferred tax assets		(496,191	)		(665,514	)
Total deferred tax assets		284			300
Total deferred tax liabilities		—			—
Net deferred tax assets	$	284		$	300

Unrecognized Tax Benefits

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

	December 31,
	2017			2016		2015
Beginning balance	$	18,413		$	17,384	$	27,522
Tax positions related to current year
Additions:
Federal		1,206			530		529
State		1,666			499		443
Reductions		—			—		—
Tax positions related to prior year
Additions:
Federal		—			—		—
State		—			—		—
Foreign		—			—		—
Reductions		(802	)		—		(11,110	)
Settlements		—			—		—
Lapses in statute of limitations		—			—		—
Ending balance	$	20,483		$	18,413	$	17,384

Segment Reporting (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Revenue by Geographic Area

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

	Year Ended December 31,
	2017		2016		2015
United States	$	190,810	$	39,147	$	40,400
Europe		116,901		126,289		190,384
Total revenue	$	307,711	$	165,436	$	230,784

Selected Quarterly Financial Data (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Data

	Year Ended December 31, 2017											Year Ended December 31, 2016
	Q1			Q2			Q3		Q4			Q1			Q2			Q3			Q4
Product sales	$	4,756		$	15,693		$	4,448	$	7,791		$	14,099		$	12,867		$	14,698		$	13,690
Total revenue	$	24,728		$	34,589		$	152,928	$	95,466		$	58,882		$	32,768		$	36,336		$	37,450
Cost of goods sold	$	6,131		$	8,989		$	5,674	$	9,753		$	8,870		$	7,708		$	7,033		$	6,604
Research and development expenses	$	61,058		$	60,260		$	65,714	$	81,429		$	49,268		$	52,350		$	51,951		$	50,232
Operating income (loss)	$	(54,437	)	$	(50,656	)	$	69,485	$	(24,034	)	$	(9,484	)	$	(38,325	)	$	(32,901	)	$	(32,145	)
Net income (loss)	$	(63,866	)	$	(59,871	)	$	60,871	$	(33,826	)	$	(19,498	)	$	(48,603	)	$	(43,224	)	$	(42,199	)
Net income (loss) per share(1)
Basic	$	(0.42	)	$	(0.39	)	$	0.39	$	(0.21	)	$	(0.14	)	$	(0.36	)	$	(0.32	)	$	(0.28	)
Diluted	$	(0.42	)	$	(0.39	)	$	0.37	$	(0.21	)	$	(0.14	)	$	(0.36	)	$	(0.32	)	$	(0.28	)

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

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) $ in Thousands, shares in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Customer Reporting_Unit shares	Dec. 31, 2016 USD ($) Customer shares	Dec. 31, 2015 shares	Jan. 01, 2017 USD ($)
Organization And Summary Of Significant Accounting Policies [Line Items]
Cash and investments in marketable securities	$ 353,220	$ 389,102
Senior secured notes	$ 250,000
Senior secured notes, maturity date	Oct. 05, 2020
Number of customers accounted for major accounts receivable \| Customer	4	3
Percentage of accounts receivable customers one	43.00%	39.00%
Percentage of accounts receivable customers two	20.00%	32.00%
Percentage of accounts receivable customers three	19.00%	13.00%
Percentage of accounts receivable customers four	14.00%
Number of reporting unit evaluated for goodwill \| Reporting_Unit	1
Minimum percentage of amount realized upon ultimate settlement	50.00%
ASC 606 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Estimated adjustment to accumulated deficit accrued royalties	$ 11,000
Adoption of New Accounting Principles [Member] \| Other Current Assets [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Impact of reclassification due to adoption of new accounting pronouncement				$ 300
Accumulated Deficit [Member] \| Adoption of New Accounting Principles [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Impact of reclassification due to adoption of new accounting pronouncement				$ 200
Federal [Member] \| Stock Option Windfall Deductions \| Adoption of New Accounting Principles [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Impact of reclassification due to adoption of new accounting pronouncement		$ 20,600
State [Member] \| Stock Option Windfall Deductions \| Adoption of New Accounting Principles [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Impact of reclassification due to adoption of new accounting pronouncement		$ 9,800
Stock Options and Restricted Stock Units [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Weighted average diluted securities excluded from diluted net loss per share \| shares	20.6	19.9	21.1
Minimum [Member] \| ASC 606 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Estimated adjustment to decrease in accumulated deficit	$ 11,000
Maximum [Member] \| ASC 606 [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Estimated adjustment to decrease in accumulated deficit	13,000
Estimated adjustment to accumulated deficit unamortized portion of upfront payment amounts recognized	$ 2,000
Buildings [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives	20 years
Manufacturing Laboratory and Other Equipment [Member] \| Minimum [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives	3 years
Manufacturing Laboratory and Other Equipment [Member] \| Maximum [Member]
Organization And Summary Of Significant Accounting Policies [Line Items]
Property and equipment estimated useful lives	10 years

Cash and Investments in Marketable Securities - Cash and Investments in Marketable Securities, Including Cash Equivalents (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and cash equivalents	$ 4,762	$ 59,640	$ 55,570	$ 12,365
Short-term investments	291,370	329,462
Long-term investments	57,088	0
Total cash and investments in marketable securities	$ 353,220	$ 389,102

- Definition

Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

+ References + Details

Cash and Investments in Marketable Securities - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Oct. 05, 2015
Cash and Investments in Marketable Securities [Line Items]
Maximum maturity term for debt securities investment	Two years or less
Weighted average maturity term for debt securities investment	One year or less
Debt investment maturity period greater than one year	$ 57,088,000	$ 0
Available-for-sale securities, sold	$ 37,549,000	4,969,000	$ 42,544,000
Senior secured notes, maturity date	Oct. 05, 2020
Level 1 to level 2 transfers	$ 0	0	0
Level 2 to level 1 transfers	0	0	$ 0
Letter of credit	$ 1,100,000	$ 2,400,000
7.75% Senior Secured Notes Due October 2020 [Member]
Cash and Investments in Marketable Securities [Line Items]
Senior secured notes, interest rate	7.75%
Senior Notes [Member] \| 7.75% Senior Secured Notes Due October 2020 [Member]
Cash and Investments in Marketable Securities [Line Items]
Senior secured notes, interest rate	7.75%			7.75%
Senior secured notes, maturity date	Oct. 05, 2020	Oct. 05, 2020
Minimum cash and investments in marketable securities to be maintained	$ 60,000,000

Cash and Investments in Marketable Securities - Portfolio of Cash and Investments in Marketable Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	$ 347,326	$ 330,713
Cash	4,460	4,355
Total cash and investments in marketable securities	353,220	389,102
Corporate Commercial Paper [Member] \| Fair Value Hierarchy Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	128,096	160,920
Corporate Notes and Bonds [Member] \| Fair Value Hierarchy Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	216,253	156,044
Obligations of U.S. government agencies [Member] \| Fair Value Hierarchy Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale investments	2,977	13,749
Money Market Funds [Member] \| Fair Value Hierarchy Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	302	51,104
Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in marketable securities	$ 1,132	$ 2,930

Inventory - Inventory (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw materials	$ 1,796	$ 2,055
Work-in-process	4,843	7,311
Finished goods	4,087	1,743
Total inventory	$ 10,726	$ 11,109

Property, Plant and Equipment - Property, Plant and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Depreciable property and equipment at cost	$ 161,153	$ 173,388
Less: accumulated depreciation and amortization	(115,090)	(111,243)
Depreciable property, plant and equipment, net	46,063	62,145
Construction-in-progress	1,400	3,456
Property plant and equipment, net	47,463	65,601
Building and Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Depreciable property and equipment at cost	81,444	75,137
Manufacturing Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciable property and equipment at cost	20,695	44,237
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciable property and equipment at cost	31,214	27,424
Furniture, Fixtures and Other Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciable property and equipment at cost	$ 27,800	$ 26,590

Property, Plant and Equipment - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation and amortization expenses		$ 12.6	$ 13.2	$ 11.4
Costs related to terminated manufacturing obligations	$ 0.9
Manufacturing Equipment [Member]
Property, Plant and Equipment [Line Items]
Original cost of impaired equipment	23.4	23.4
Net book value of impaired equipment	$ 15.1	$ 15.1

Senior Secured Notes - Additional Information (Detail) - USD ($)		12 Months Ended
	Oct. 05, 2015	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Secured Notes [Line Items]
Senior secured notes, maturity date		Oct. 05, 2020
Cash paid for interest		$ 20,116,000	$ 20,589,000	$ 20,225,000
Loss on extinguishment of debt		0	0	14,079,000
Write-off of unamortized issuance costs		$ 0	$ 0	1,579,000
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 secured notes, principal amount		$ 250,000,000
7.75% Senior Secured Notes Due October 2020 [Member]
Secured Notes [Line Items]
Senior secured notes, interest rate		7.75%
Senior Notes [Member] \| 7.75% Senior Secured Notes Due October 2020 [Member]
Secured Notes [Line Items]
Senior secured notes, issued	$ 250,000,000
Senior secured notes, interest rate	7.75%	7.75%
Senior secured notes, maturity date		Oct. 05, 2020	Oct. 05, 2020
Frequency of payment		Quarterly
Issuance costs	$ 8,900,000
Debt discount on transaction and facility fees	8,700,000
Unamortized debt discount and issuance costs		$ 4,800,000
Debt instrument term		5 years
Senior secured notes, cash received	$ 100,300,000
Minimum cash and investments in marketable securities to be maintained		$ 60,000,000
Senior Notes [Member] \| 7.75% Senior Secured Notes Due October 2020 [Member] \| Level 3 [Member]
Secured Notes [Line Items]
Senior secured notes, principal amount		$ 250,000,000
Senior Notes [Member] \| 12% Senior Secured Notes Due July 2017 [Member]
Secured Notes [Line Items]
Senior secured notes, interest rate	12.00%
Senior secured notes, maturity date	Jul. 15, 2017
Repayment of senior secured notes	$ 125,000,000
Accrued interest paid on 12% notes at redemption	3,300,000
Redemption premium	12,500,000			11,300,000
Cash paid for interest	$ 1,200,000			1,200,000
Loss on extinguishment of debt				14,100,000
Write-off of unamortized issuance costs				$ 1,600,000

Leases - Additional Information (Detail)	1 Months Ended	12 Months Ended
Leases - Additional Information (Detail)	Aug. 31, 2017 ft² yr	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Leases [Line Items]
Rent expense		$ 4,700,000	$ 3,200,000	$ 3,200,000
Deferred rent		6,000,000	6,600,000
Repayment of capital lease		5,131,000	$ 5,945,000	$ 5,187,000
Capital lease balance		$ 0
ARE-San Francisco No. 19, LLC [Member]
Leases [Line Items]
Extended lease term start year	2020
Lease expiration year	2030
Lease space \| ft²	129,732
Lease description option to extend		The term of the Lease commenced on September 1, 2017, and will expire January 31, 2030, subject to our right to extend the term of the Lease for two consecutive five-year periods.
Number of consecutive 5 year terms to extend lease \| yr	2
Lease extension term	5 years
Lease commencement date	Sep. 01, 2017
Lease expiration date	Jan. 31, 2030
Additional space required to be leased in the future \| ft²	23,000

Leases - Future Minimum Lease Payments for Operating Leases (Detail) $ in Thousands	Dec. 31, 2017 USD ($)
Leases [Abstract]
2018	$ 5,965
2019	5,511
2020	5,884
2021	8,739
2022	9,024
2023 and thereafter	71,127
Total future minimum lease payments	$ 106,250

Liability Related to the Sale of Future Royalties - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended		3 Months Ended	12 Months Ended			70 Months Ended
	Feb. 24, 2012	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
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					$ 30,531	$ 30,158	$ 22,058	$ 137,531
Non-cash interest expense on liability related to sale of future royalties					$ 18,869	$ 19,712	$ 20,619	$ 120,453
Annual interest rate				17.60%				17.00%
Prospective interest rate				21.00%
Purchase and Sale Agreement with RPI [Member]
Liability Related to the Sale of Future Royalties [Line Items]
Proceeds from sale of royalty rights	$ 124,000
Transaction costs related to sale of potential future royalties	$ 4,400
Payment made for milestone not achieved year two		$ 7,000
Payment made for milestone not achieved year one			$ 3,000

Liability Related to the Sale of Future Royalties - Summary of Liability Related to Potential Future Royalties (Detail) - USD ($) $ in Thousands	12 Months Ended			70 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017
Other Liabilities Disclosure [Abstract]
Liability related to the sale of future royalties—beginning balance	$ 108,584			$ 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	(30,531)	$ (30,158)	$ (22,058)	(137,531)
Non-cash interest expense recognized	18,869	19,712	$ 20,619	120,453
Liability related to the sale of future royalties – ending balance	96,922	108,584		96,922
Less: unamortized transaction costs	(2,267)			(2,267)
Liability related to the sale of future royalties, net	$ 94,655	$ 105,950		$ 94,655

Commitments and Contingencies - Additional Information (Detail) - USD ($)			1 Months Ended		12 Months Ended
	Jun. 30, 2017	Jun. 26, 2017	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 14, 2015
Loss Contingencies [Line Items]
Purchase commitments related to contract manufacturing, clinical development and certain other items			$ 16,500,000		$ 16,500,000
Royalty expense					3,100,000	$ 3,700,000	$ 2,800,000
Indemnification Obligation [Member]
Loss Contingencies [Line Items]
Litigation matters, liabilities			0		0	0
Merger and Acquisition Related Claims [Member]
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident			1,800,000		1,800,000
Securities Related Claims [Member]
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident			1,800,000		1,800,000
Non-Securities Related Claims [Member]
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident			500,000		500,000
Cross-License Agreement [Member]
Loss Contingencies [Line Items]
Total payments due related to license agreement amendment		$ 7,000,000
Payment made related to license agreement amendment			3,500,000	$ 3,500,000
Litigation matters, prepayment of royalty obligations for future commercial sales	$ 2,300,000
Litigation matters, liabilities						$ 0
Cross-License Agreement [Member] \| Cost of Goods Sold [Member]
Loss Contingencies [Line Items]
Accrued royalties for commercial sales			1,400,000		1,400,000
Cross-License Agreement [Member] \| General and Administrative Expense [Member]
Loss Contingencies [Line Items]
Accrued expense related to license agreement amendment					3,300,000
Cross-License Agreement [Member] \| Other Current Assets [Member]
Loss Contingencies [Line Items]
Unamortized prepaid royalty			$ 600,000		$ 600,000
Enzon Litigation [Member]
Loss Contingencies [Line Items]
Damage claim for alleged unpaid licenses								$ 1,500,000
Enzon Litigation [Member] \| Cross-License Agreement [Member]
Loss Contingencies [Line Items]
Litigation matters, dismissal date					Jun. 30, 2017

Stockholders' Equity - Additional Information (Detail) - USD ($)		12 Months Ended
	Oct. 24, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class of Stock [Line Items]
Preferred stock, shares authorized		10,000,000	10,000,000
Preferred stock, par value		$ 0.0001	$ 0.0001
Preferred stock, shares designated		0	0
Preferred stock, shares issued		0	0
Preferred stock, shares outstanding		0	0
Proceeds from sale of common stock	$ 189,700,000
Common stock, shares authorized		300,000,000	300,000,000
Maximum 401(k) per employee, percentage of annual salary		60.00%
Matching 401(k) employer contribution, maximum amount		$ 4,000
Compensation expense in connection with 401(k) retirement plan		$ 1,600,000	$ 1,100,000	$ 900,000
Change in control severance payment period for executives		12 months
Change in control severance payment period for employees		6 months
Change in control cash severance payment for chief executive officer		24 months base salary plus annual target incentive pay
Employee Stock Purchase Plan [Member]
Class of Stock [Line Items]
Common stock, shares authorized		2,500,000
Percentage of purchase price of stock		85.00%
2017 Performance Incentive Plan [Member]
Class of Stock [Line Items]
Number of common stock shares available for stock options grants		8,300,000
Share-based compensation plan's share limit reduction for every one restricted stock unit granted		1.5
Stock options term under equity incentive plans		8 years
2017 Performance Incentive Plan [Member] \| Director [Member]
Class of Stock [Line Items]
Service period for stock-based compensation award granted		1 year
2017 Performance Incentive Plan [Member] \| Stock Options [Member] \| Employee [Member]
Class of Stock [Line Items]
Service period for stock-based compensation award granted		4 years
2017 Performance Incentive Plan [Member] \| Stock Options [Member] \| Director [Member]
Class of Stock [Line Items]
Service period for stock-based compensation award granted		1 year
2017 Performance Incentive Plan [Member] \| Restricted Stock Units (RSU) [Member] \| Employee [Member]
Class of Stock [Line Items]
Service period for stock-based compensation award granted		3 years
Common Shares [Member]
Class of Stock [Line Items]
Sale of common stock, Shares	14,950,000		14,950,000
Underwriting commissions and discounts	$ 12,100,000
Legal, accounting fees, filing fees and other offering expenses	$ 400,000
Common stock, shares reserved for issuance in equity compensation plans		26,761,122

Stockholders' Equity - Summarization of Common Stock Shares for Issuance Under Existing Equity Compensation Plans (Detail) shares in Thousands	Dec. 31, 2017 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Securities to be Issued Upon Exercise of Outstanding Options & Vesting of RSUs	21,401
Weighted-Average Exercise Price of Outstanding Options \| $ / shares	$ 20.35
Number of Securities Remaining Available for Issuance Under Equity Compensation Plans (Excluding Securities Reflected in Column)	5,360
Equity Compensation Plans Approved by Security Holders [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Securities to be Issued Upon Exercise of Outstanding Options & Vesting of RSUs	20,999
Weighted-Average Exercise Price of Outstanding Options \| $ / shares	$ 20.55
Number of Securities Remaining Available for Issuance Under Equity Compensation Plans (Excluding Securities Reflected in Column)	5,360
Equity Compensation Plans Not Approved by Security Holders [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Securities to be Issued Upon Exercise of Outstanding Options & Vesting of RSUs	402
Weighted-Average Exercise Price of Outstanding Options \| $ / shares	$ 11.01
Number of Securities Remaining Available for Issuance Under Equity Compensation Plans (Excluding Securities Reflected in Column)	0

License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 210,965	$ 60,382	$ 165,604
Eli Lilly and Company [Member] \| NKTR-358 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	130,087
Ophthotech Corporation [Member] \| Fovista [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	19,123	1,408	1,398
Bayer Healthcare LLC [Member] \| BAY41-6551 (Amikacin Inhale) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	17,931	1,429	1,919
Baxalta Incorporated/Shire [Member] \| ADYNOVATE [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	11,443	650	10,694
MAP Pharmaceuticals, Inc. / Allergan [Member] \| SEMPRANA [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	11,000
Amgen, Inc. [Member] \| Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	5,000	5,000	5,000
AstraZeneca AB [Member] \| MOVANTIK and MOVANTIK fixed-dose combination program [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	4,600	33,000	130,000
Daiichi Sankyo Europe GmbH [Member] \| ONZEALDTM (NKTR-102) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	3,811	3,690
Roche [Member] \| PEGASYS and MIRCERA [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue		7,685	12,816
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 7,970	$ 7,520	$ 3,777

License and Collaboration Agreements - Additional Information (Detail) - USD ($)				1 Months Ended												3 Months Ended		12 Months Ended
	Aug. 23, 2017	Sep. 21, 2016	Mar. 01, 2016	Dec. 31, 2017	Nov. 30, 2017	Sep. 30, 2017	Jan. 31, 2017	Aug. 31, 2016	Apr. 30, 2016	Nov. 30, 2015	Aug. 31, 2015	Mar. 31, 2015	Jun. 30, 2014	Feb. 29, 2012	Jan. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2013	Dec. 31, 2007	Jul. 31, 2016	Jul. 31, 2015
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones																		$ 305,500,000
Liability related to refundable upfront payment				$ 0														0	$ 12,500,000
Settlement Agreement with Allergan, Inc and Map Pharmaceuticals, Inc [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue				0														0
License revenue received related to share of payments due																		11,000,000
Gain on settlement agreement represents reimbursement of legal expenses																		$ 4,000,000
Nektar's [Member] \| NKTR-358 [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of sharing in Phase 2 development costs	25.00%
Nektar's [Member] \| AstraZeneca-Kirin [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of upfront payment, market access milestones, royalties and sales milestones			40.00%
Eli Lilly and Company [Member] \| NKTR-358 [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment						$ 150,000,000
Percentage of sharing in Phase 2 development costs	75.00%
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.
Revenue related to Phase 1 clinical development and drug development activities																		$ 4,200,000
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| License [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment																		125,900,000
Revenue related to license activities																		125,900,000
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| Phase 1 Clinical Development [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment																		17,600,000
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| Drug Product Development [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment																		6,500,000
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| Phase 1 Clinical Development and Drug Product Development [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue				19,900,000														19,900,000
Eli Lilly and Company [Member] \| NKTR-358 [Member] \| Maximum [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional development and regulatory milestones	$ 250,000,000
Eli Lilly and Company [Member] \| Nektar's [Member] \| NKTR-358 [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of development milestones payments, to be received may be reduced under certain conditions	50.00%
Percentage of development milestones payments, to be received will be reduced if conditions occur	75.00%
Eli Lilly and Company [Member] \| Nektar's [Member] \| NKTR-358 [Member] \| Maximum [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of funding phase 3 development costs on an indication by indication basis borne	25.00%
Eli Lilly and Company [Member] \| Nektar's [Member] \| NKTR-358 [Member] \| Minimum [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of funding phase 3 development costs on an indication by indication basis borne	0.00%
Ophthotech Corporation [Member]
Deferred Revenue Arrangement [Line Items]
Advance payment from collaboration partner							$ 12,700,000
Ophthotech Corporation [Member] \| Reagent Shipments [Member]
Deferred Revenue Arrangement [Line Items]
Advance payment from collaboration partner for reagent shipments							$ 10,400,000
Ophthotech Corporation [Member] \| Minimum Purchase Requirement [Member]
Deferred Revenue Arrangement [Line Items]
Advance payment from collaboration partner																		2,300,000
Ophthotech Corporation [Member] \| Fovista [Member]
Deferred Revenue Arrangement [Line Items]
Recognition of remaining deferred revenue																		18,000,000
Ophthotech Corporation [Member] \| Fovista [Member] \| Novartis Pharma AG [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment													$ 19,800,000
Bayer Healthcare LLC [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment																						$ 40,000,000
Bayer Healthcare LLC [Member] \| Performance-based Milestone Payments [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment																					$ 30,000,000
Recognition of remaining deferred revenue																		16,800,000
Baxalta Incorporated [Member] \| ADYNOVATE (Hemophilia) [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue				1,000,000														1,000,000
Development milestones achieved										$ 10,000,000
Received under right to sublicense agreement					$ 12,000,000
Allocated consideration for ongoing supply obligation																		1,000,000
Consideration received for right to sublicense																		11,000,000
Baxalta Incorporated [Member] \| ADYNOVATE (Hemophilia) [Member] \| European Union [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones																		10,000,000
MAP Pharmaceuticals, Inc. [Member] \| MAP-Allergan, Inc. [Member]
Deferred Revenue Arrangement [Line Items]
Upfront and milestone payments received by Our collaboration partner under sublicense arrangement															$ 80,000,000
Allergan, Inc. [Member] \| Settlement Agreement with Allergan, Inc and Map Pharmaceuticals, Inc [Member]
Deferred Revenue Arrangement [Line Items]
Payment received under settlement agreement for relief of claims related to share																		15,000,000
Amgen, Inc. [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment																$ 50,000,000
Deferred revenue				14,200,000														14,200,000
AstraZeneca AB [Member] \| United States [Member]
Deferred Revenue Arrangement [Line Items]
Liability to AZ for DTC advertising payments												$ 10,000,000											$ 5,000,000	$ 5,000,000
Reduction of revenue																				$ (10,000,000)
AstraZeneca AB [Member] \| MOVANTIK and MOVANTIK fixed-dose combination program [Member] \| Upfront Payment Arrangement [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment																	$ 125,000,000
AstraZeneca AB [Member] \| MOVANTIK Fixed-dose Combination Program [Member]
Deferred Revenue Arrangement [Line Items]
Potential contingent payments based on development events				75,000,000														75,000,000
AstraZeneca AB [Member] \| MOVANTIK [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment												$ 100,000,000
AstraZeneca AB [Member] \| MOVANTIK [Member] \| European Union [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment											$ 40,000,000
AstraZeneca AB [Member] \| AstraZeneca-Kirin [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment									$ 28,000,000									4,600,000	33,000,000
Deferred revenue				0														0
Upfront and milestone payments received by Our collaboration partner under sublicense arrangement			$ 70,000,000
Percentage of upfront milestones royalty and sales milestone payments from sublicense agreement retained by our collaboration partner			60.00%
Daiichi Sankyo Europe GmbH [Member] \| ONZEALDTM (NKTR-102) [Member]
Deferred Revenue Arrangement [Line Items]
Refundable upfront payment paid				12,500,000														12,500,000
Liability related to refundable upfront payment																			12,500,000
Non-refundable portion of upfront payment																			7,500,000
Revenue recognized from upfront payment																			3,700,000
Daiichi Sankyo Europe GmbH [Member] \| ONZEALDTM (NKTR-102) [Member] \| Upfront Payment Arrangement [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment								$ 20,000,000
Recognition of remaining deferred revenue																		$ 3,200,000
Roche [Member] \| MIRCERA [Member]
Deferred Revenue Arrangement [Line Items]
Consideration received for product delivered																					$ 18,600,000
Roche [Member] \| MIRCERA [Member] \| Upfront Payment Arrangement [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payment														$ 27,000,000
Roche [Member] \| PEGASYS and MIRCERA [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue																			$ 0
Bristol-Myers Squibb [Member]
Deferred Revenue Arrangement [Line Items]
Strategic collaboration agreement date																		Feb. 13, 2018
Bristol-Myers Squibb [Member] \| NKTR-214 [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of out-of-pocket costs reimbursed by partner		50.00%
Payments received for reimbursement of costs																		$ 7,800,000
License agreement exclusivity expiration date																		Sep. 30, 2018
License agreement exclusivity negotiation period																		3 months
Other [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones																		$ 45,500,000
Deferred revenue				$ 2,900,000														$ 2,900,000

Stock-Based Compensation - Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 36,615	$ 25,850	$ 19,669
Cost of Goods Sold [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	2,333	1,620	1,142
Research and Development Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	21,252	13,093	9,207
General and Administrative Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 13,030	$ 11,137	$ 9,320

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation costs	$ 211.8
Recognized over a weighted-average period	2 years 1 month 6 days
Dividend yield	0.00%	0.00%	0.00%
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield				0.00%
Weighted-average grant-date fair value	$ 20.08	$ 6.54	$ 6.55
Total intrinsic value of options exercised	$ 84.0	$ 17.9	$ 20.5
Estimated fair value of options vested	$ 19.3	$ 16.7	$ 16.8

Stock-Based Compensation - Black-Scholes Option-Pricing Model Assumptions Used to Calculate Fair Value of Employee Stock Options (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Average risk-free interest rate	2.00%	1.40%	1.60%
Dividend yield	0.00%	0.00%	0.00%
Average volatility factor	54.20%	51.70%	50.80%
Average weighted average expected life	5 years 3 months 18 days	5 years 3 months 18 days	5 years 3 months 18 days

Stock-Based Compensation - Stock Option Activity Under Equity Incentive Plans (Detail) - Stock Options [Member] $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares, Outstanding, Beginning balance \| shares	19,413
Number of Shares, Options granted \| shares	5,322
Number of Shares, Options exercised \| shares	(5,284)
Number of Shares, Options forfeited and canceled \| shares	(625)
Number of Shares, Outstanding, Ending balance \| shares	18,826
Number of Shares, Exercisable \| shares	10,504
Weighted-Average Exercise Price per Share, Outstanding, Beginning balance \| $ / shares	$ 12.01
Weighted-Average Exercise Price per Share, Options granted \| $ / shares	40.56
Weighted-Average Exercise Price per Share, Options exercised \| $ / shares	10.88
Weighted-Average Exercise Price per Share, Options forfeited and Canceled \| $ / shares	13.69
Weighted-Average Exercise Price per Share, Outstanding, Ending balance \| $ / shares	20.35
Weighted-Average Exercise Price per Share, Exercisable \| $ / shares	$ 11.95
Weighted-Average Remaining Contractual Life, Outstanding	5 years 1 month 24 days
Weighted-Average Remaining Contractual Life, Exercisable	3 years 6 months 25 days
Aggregate Intrinsic Value, Outstanding \| $	$ 741,257
Aggregate Intrinsic Value, Exercisable \| $	$ 501,818

Stock-Based Compensation - Restricted Stock Unit Award Activity (Detail) - Restricted Stock Units (RSU) [Member] $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Units Issued, Beginning balance \| shares	2,248
Granted \| shares	1,405
Vested and released \| shares	(875)
Forfeited and canceled \| shares	(200)
Units Issued, Ending balance \| shares	2,578
Weighted Average Grant Date Fair Value, Beginning balance \| $ / shares	$ 13.53
Weighted Average Grant Date Fair Value, Granted \| $ / shares	54.14
Weighted Average Grant Date Fair Value, Vested and released \| $ / shares	14.05
Weighted Average Grant Date Fair Value, Forfeited and canceled \| $ / shares	13.14
Weighted Average Grant Date Fair Value, Ending balance \| $ / shares	$ 35.52
Aggregate Intrinsic Value, Ending balance \| $	$ 153,941

Income Taxes - Loss Before Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic	$ (97,938)	$ (155,375)	$ (81,931)
Foreign	1,862	2,727	1,260
Loss before provision for income taxes	$ (96,076)	$ (152,648)	$ (80,671)

Income Taxes - Provision for Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal	$ 0	$ 0	$ 0
State	1	(1)	(1)
Foreign	580	992	529
Total Current	581	991	528
Deferred:
Federal	0	0	0
State	0	0	0
Foreign	35	(115)	(22)
Total Deferred	35	(115)	(22)
Provision for income taxes	$ 616	$ 876	$ 506

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes Disclosure [Line Items]
Statutory income tax rate		35.00%
Valuation allowance, increase (decrease) amount		$ (169,300,000)	$ 52,500,000	$ 17,300,000
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		8,038,000	$ 4,543,000	$ 4,529,000
Federal orphan drug credits		$ 17,700,000
Federal orphan drug credits, expiration year		2026
Unrecognized tax benefits, period may increase or decrease due to tax examination		Next twelve months
Federal [Member]
Income Taxes Disclosure [Line Items]
Net operating loss carryforward for income tax		$ 1,610,300,000
Net operating loss carryforward, expiration year		2018
Income tax research credits		$ 64,000,000
Income tax research credits, expiration year		2019
State [Member]
Income Taxes Disclosure [Line Items]
Net operating loss carryforward for income tax		$ 474,000,000
Net operating loss carryforward, expiration year		2019
Income tax research credits		$ 33,300,000
Scenario Forecast [Member]
Income Taxes Disclosure [Line Items]
Statutory income tax rate	21.00%

Income Taxes - Income Tax Provision Related to Continuing Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
U.S. federal provision (benefit)
At statutory rate	$ (33,627)	$ (53,427)	$ (28,235)
Tax law changes	248,155	0	0
Non-cash interest expense on liability related to sale of future royalties	6,604	6,899	7,217
Non-deductible officers' compensation	2,547	220	184
Change in valuation allowance	(186,124)	51,981	22,210
Stock-based compensation	(20,665)	528	674
Sale of future royalties	(8,236)	0	0
Research credits	(8,038)	(4,543)	(4,529)
Foreign tax deduction	0	0	1,773
Other	0	(782)	1,212
Provision for income taxes	$ 616	$ 876	$ 506

Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Net operating loss carryforwards	$ 364,864	$ 508,406
Research and other credits	94,103	74,917
Stock-based compensation	14,552	26,357
Property, plant and equipment	6,848	6,882
Reserves and accruals	5,659	12,269
Capitalized research expenses	5,497	11,587
Deferred revenue	3,796	23,035
Sale of future royalties	0	1,611
Other	1,156	750
Deferred tax assets before valuation allowance	496,475	665,814
Valuation allowance for deferred tax assets	(496,191)	(665,514)
Total deferred tax assets	284	300
Total deferred tax liabilities	0	0
Net deferred tax assets	$ 284	$ 300

Income Taxes - Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Beginning balance	$ 18,413	$ 17,384	$ 27,522
Reductions	0	0	0
Reductions	(802)	0	(11,110)
Settlements	0	0	0
Lapses in statute of limitations	0	0	0
Ending balance	20,483	18,413	17,384
Federal [Member]
Income Tax Contingency [Line Items]
Tax positions related to current year, Additions	1,206	530	529
Tax positions related to prior year, Additions	0	0	0
State [Member]
Income Tax Contingency [Line Items]
Tax positions related to current year, Additions	1,666	499	443
Tax positions related to prior year, Additions	0	0	0
Foreign [Member]
Income Tax Contingency [Line Items]
Tax positions related to prior year, Additions	$ 0	$ 0	$ 0

Segment Reporting - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) Segment	Dec. 31, 2016 USD ($)	Dec. 31, 2015
Segment Reporting Information [Line Items]
Number of operating business segment \| Segment	1
Property, plant and equipment, net	$ 47,463	$ 65,601
United States [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 41,700	$ 48,800
Percentage of net book value of property and equipment	88.00%	74.00%
India [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 5,800	$ 5,600
Percentage of net book value of property and equipment	12.00%	9.00%
Germany and Netherlands [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net		$ 10,400
Percentage of net book value of property and equipment		16.00%
Other Countries [Member]
Segment Reporting Information [Line Items]
Property, plant and equipment, net		$ 800
Percentage of net book value of property and equipment		1.00%
Revenue [Member] \| Eli Lilly & Co [Member] \| Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage revenue from clients	42.00%
Revenue [Member] \| UCB [Member] \| Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage revenue from clients	12.00%	21.00%	13.00%
Revenue [Member] \| AstraZeneca [Member] \| Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage revenue from clients		29.00%	57.00%
Revenue [Member] \| Ophthotech Corporation [Member] \| Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage revenue from clients		19.00%
Revenue [Member] \| Roche [Member] \| Customer Concentration Risk [Member]
Segment Reporting Information [Line Items]
Percentage revenue from clients		11.00%

Segment Reporting - Revenue by Geographic Area (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue by geographic area
Total revenue	$ 95,466	$ 152,928	$ 34,589	$ 24,728	$ 37,450	$ 36,336	$ 32,768	$ 58,882	$ 307,711	$ 165,436	$ 230,784
United States [Member] \| Reportable Geographical Components [Member]
Revenue by geographic area
Total revenue									190,810	39,147	40,400
European [Member] \| Reportable Geographical Components [Member]
Revenue by geographic area
Total revenue									$ 116,901	$ 126,289	$ 190,384

Subsequent Event - Additional Information (Detail) - Subsequent Event [Member]	Feb. 13, 2018 USD ($) $ / shares shares
Purchase Agreement [Member]
Subsequent Event [Line Items]
Shares expected to be issued in future period \| shares	8,284,600
Sale of stock consideration expected to be received in future period	$ 850,000,000
Issued price per share \| $ / shares	$ 102.60
Subsequent event, description	The closings of the BMS Collaboration Agreement and the Purchase Agreement will be simultaneous and are expected to occur during the second quarter of 2018
NKTR-214 [Member] \| Nektar's [Member]
Subsequent Event [Line Items]
Global commercialization profits and losses sharing percentage	65.00%
NKTR-214 [Member] \| Bristol-Myers Squibb [Member]
Subsequent Event [Line Items]
Non-refundable upfront payment to be received in cash in future period	$ 1,000,000,000
Global commercialization profits and losses sharing percentage	35.00%
NKTR-214 [Member] \| Maximum [Member] \| Bristol-Myers Squibb [Member]
Subsequent Event [Line Items]
Maximum total additional cash payments receivable upon achievement of certain development and regulatory milestones	$ 1,430,000,000
Eligible additional cash payments receivable upon achievement of certain sales milestones	$ 350,000,000

Selected Quarterly Financial Data - Quarterly Financial Data (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Product sales	$ 7,791	$ 4,448	$ 15,693	$ 4,756	$ 13,690	$ 14,698	$ 12,867	$ 14,099	$ 32,688	$ 55,354	$ 40,155
Total revenue	95,466	152,928	34,589	24,728	37,450	36,336	32,768	58,882	307,711	165,436	230,784
Cost of goods sold	9,753	5,674	8,989	6,131	6,604	7,033	7,708	8,870	30,547	30,215	34,102
Research and development expenses	81,429	65,714	60,260	61,058	50,232	51,951	52,350	49,268	268,461	203,801	182,787
Operating income (loss)	(24,034)	69,485	(50,656)	(54,437)	(32,145)	(32,901)	(38,325)	(9,484)	(59,642)	(112,855)	(29,371)
Net income (loss)	$ (33,826)	$ 60,871	$ (59,871)	$ (63,866)	$ (42,199)	$ (43,224)	$ (48,603)	$ (19,498)	$ (96,692)	$ (153,524)	$ (81,177)
Net income (loss) per share
Basic	$ (0.21)	$ 0.39	$ (0.39)	$ (0.42)	$ (0.28)	$ (0.32)	$ (0.36)	$ (0.14)
Diluted	$ (0.21)	$ 0.37	$ (0.39)	$ (0.42)	$ (0.28)	$ (0.32)	$ (0.36)	$ (0.14)

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

Consolidated Statements of Cash Flows (Parenthetical)	Dec. 31, 2017
7.75% Senior Secured Notes [Member]
Senior secured notes, interest rate	7.75%
12% Senior Secured Notes [Member]
Senior secured notes, interest rate	12.00%

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

Stock-Based Compensation - Restricted Stock Unit Award Activity (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2017 $ / shares
Restricted Stock Units (RSU) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grant price of the award	$ 0