Document and Entity Information (USD $)	12 Months Ended
Document and Entity Information (USD $)	Dec. 31, 2011	Feb. 24, 2012	Jun. 30, 2011
Document and Entity Information [Abstract]
Entity Registrant Name	NEKTAR THERAPEUTICS
Entity Central Index Key	0000906709
Document Type	10-K
Document Period End Date	Dec. 31, 2011
Amendment Flag	false
Document Fiscal Year Focus	2011
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 827,788,677
Entity Common Stock, Shares Outstanding		114,530,745

Consolidated Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Current assets:
Cash and cash equivalents	$ 15,312	$ 17,755
Short-term investments	225,856	298,177
Accounts receivable, net of allowance of nil at December 31, 2011 and 2010	4,938	25,102
Inventory	12,656	7,266
Other current assets	17,944	5,679
Total current assets	276,706	353,979
Long-term investments	173,768
Property and equipment, net	78,576	89,773
Goodwill	76,501	76,501
Other assets	999	972
Total assets	606,550	521,225
Current liabilities:
Accounts payable	3,019	7,194
Accrued compensation	12,807	9,252
Accrued expenses	6,669	8,540
Accrued clinical trial expenses	11,953	12,144
Deferred revenue, current portion	19,643	20,584
Convertible subordinated notes, current portion	214,955
Other current liabilities	6,486	6,394
Total current liabilities	275,532	64,108
Convertible subordinated notes		214,955
Capital lease obligations, less current portion	14,582	17,014
Deferred revenue, less current portion	108,188	124,763
Deferred gain	3,278	4,152
Other long-term liabilities	7,159	5,571
Total liabilities	408,739	430,563
Commitments and contingencies
Stockholders' equity:
Preferred stock, 10,000 shares authorized Series A, $0.0001 par value; 3,100 shares designated; no shares issued or outstanding at either December 31, 2011 or 2010
Common stock, $0.0001 par value; 300,000 authorized; 114,485 shares and 94,517 shares issued and outstanding at December 31, 2011 and 2010, respectively	11	9
Capital in excess of par value	1,597,428	1,354,232
Accumulated other comprehensive (loss) income	(1,103)	968
Accumulated deficit	(1,398,525)	(1,264,547)
Total stockholders' equity	197,811	90,662
Total liabilities and stockholders' equity	$ 606,550	$ 521,225

Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets [Abstract]
Allowances for accounts receivable
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized Series A	10,000	10,000
Preferred stock, shares designated	3,100	3,100
Preferred stock, shares issued
Preferred stock, shares outstanding
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	300,000	300,000
Common stock, shares issued	114,485	94,517
Common stock, shares outstanding	114,485	94,517

Consolidated Statements of Operations (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Revenue:
Product sales	$ 24,864	$ 27,412	$ 30,116
Royalty revenues	10,327	7,255	5,172
License, collaboration and other revenue	36,289	124,372	36,643
Total revenue	71,480	159,039	71,931
Operating costs and expenses:
Cost of goods sold	21,891	25,667	30,948
Research and development	126,766	108,065	95,109
General and administrative	46,760	40,986	41,006
Impairment of long-lived assets	0	12,576	0
Total operating costs and expenses	195,417	187,294	167,063
Loss from operations	(123,937)	(28,255)	(95,132)
Non-operating income (expense):
Interest income	2,244	1,545	3,688
Interest expense	(10,223)	(11,174)	(12,176)
Other income (expense), net	(1,044)	827	848
Total non-operating expense, net	(9,023)	(8,802)	(7,640)
Loss before provision (benefit) for income taxes	(132,960)	(37,057)	(102,772)
Provision (benefit) for income taxes	1,018	881	(253)
Net loss	$ (133,978)	$ (37,938)	$ (102,519)
Basic and diluted net loss per share	$ (1.19)	$ (0.40)	$ (1.11)
Weighted average shares outstanding used in computing basic and diluted net loss per share	112,942	94,079	92,772

Consolidated Statements of Stockholders' Equity (USD $) In Thousands	Common Stock	Capital in Excess of Par Value	Accumulated Other Comprehensive Income/(Loss)	Accumulated Deficit	Total
Beginning Balance at Dec. 31, 2008	$ 9	$ 1,312,796	$ 1,439	$ (1,124,090)	$ 190,154
Beginning Balance, Shares at Dec. 31, 2008	92,503
Stock option exercises and RSU release		4,696			4,696
Stock option exercises and RSU release, Shares	742
Stock-based compensation		10,326			10,326
Shares issued for Employee Stock Purchase Plan		124			124
Shares issued for Employee Stock Purchase Plan, Shares	36
Other comprehensive loss			(414)		(414)
Net loss				(102,519)	(102,519)
Comprehensive loss					(102,933)
Ending Balance at Dec. 31, 2009	9	1,327,942	1,025	(1,226,609)	102,367
Ending Balance, Shares at Dec. 31, 2009	93,281
Stock option exercises and RSU release		8,340			8,340
Stock option exercises and RSU release, Shares	1,176
Stock-based compensation		17,399			17,399
Shares issued for Employee Stock Purchase Plan		551			551
Shares issued for Employee Stock Purchase Plan, Shares	60
Other comprehensive loss			(57)		(57)
Net loss				(37,938)	(37,938)
Comprehensive loss					(37,995)
Ending Balance at Dec. 31, 2010	9	1,354,232	968	(1,264,547)	90,662
Ending Balance, Shares at Dec. 31, 2010	94,517				94,517
Sale of common stock, net of issuance costs of $617	2	219,781			219,783
Sale of common stock, net of issuance costs of $617, shares	19,000
Stock option exercises and RSU release		3,916			3,916
Stock option exercises and RSU release, Shares	866
Stock-based compensation		18,885			18,885
Shares issued for Employee Stock Purchase Plan		614			614
Shares issued for Employee Stock Purchase Plan, Shares	102
Other comprehensive loss			(2,071)		(2,071)
Net loss				(133,978)	(133,978)
Comprehensive loss					(136,049)
Ending Balance at Dec. 31, 2011	$ 11	$ 1,597,428	$ (1,103)	$ (1,398,525)	$ 197,811
Ending Balance, Shares at Dec. 31, 2011	114,485				114,485

Consolidated Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cash flows from operating activities:
Net loss	$ (133,978)	$ (37,938)	$ (102,519)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	14,951	16,551	14,881
Stock-based compensation	18,885	17,399	10,326
Impairment of long-lived assets	0	12,576	0
Other non-cash transactions	1,359	198	(657)
Changes in assets and liabilities:
Accounts receivable	20,164	(20,301)	6,034
Inventory	(5,390)	(795)	2,848
Other assets	(12,267)	577	(200)
Accounts payable	(3,384)	4,274	(8,046)
Accrued compensation	3,555	(800)	(1,518)
Accrued expenses	1,013	1,683	(4,191)
Accrued clinical trial expenses	(191)	(2,023)	(3,455)
Deferred revenue	(17,516)	(47,025)	126,795
Other liabilities	(943)	(247)	(559)
Net cash (used in) provided by operating activities	(113,742)	(55,871)	39,739
Cash flows from investing activities:
Purchases of property and equipment	(9,722)	(31,457)	(16,390)
Advance payments for property and equipment			(4,312)
Maturities of investments	383,052	475,813	310,707
Sales of investments	210,089	15,479	17,318
Purchases of investments	(695,371)	(443,122)	(451,918)
Transaction costs for sale of pulmonary assets			(4,440)
Net cash (used in) provided by investing activities	(111,952)	16,713	(149,035)
Cash flows from financing activities:
Issuance of common stock, net of issuance costs	224,313	8,891	4,820
Payments of loan and capital lease obligations	(1,978)	(1,356)	(1,285)
Net cash provided by financing activities	222,335	7,535	3,535
Effect of exchange rates on cash and cash equivalents	916	(219)	(226)
Net decrease in cash and cash equivalents	(2,443)	(31,842)	(105,987)
Cash and cash equivalents at beginning of year	17,755	49,597	155,584
Cash and cash equivalents at end of year	15,312	17,755	49,597
Supplemental disclosure of cash flows information:
Cash paid for interest	10,277	10,599	11,225
Cash paid for income taxes	957	407	743
Supplemental schedule of non-cash investing and financing activities:
Property and equipment acquired through capital leases		$ 195

Organization and Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2011

Organization and Summary of Significant Accounting Policies [Abstract]

Organization and Summary of Significant Accounting Policies

Note 1 — Organization and Summary of Significant Accounting Policies

Organization

We are a clinical-stage biopharmaceutical company headquartered in San Francisco, California and incorporated in Delaware. We are developing a pipeline of drug candidates that utilize our PEGylation and advanced polymer conjugate technology platforms designed to improve the therapeutic benefits of drugs.

Our development activities have required significant resources to date and are expected to continue to require significant resources. As a result, we expect to continue to incur substantial losses and negative cash flows from operations in the future. Historically, we have financed our operations primarily through cash from licensing, collaboration and manufacturing agreements and public and private placements of debt and equity securities. At December 31, 2011, we had approximately $414.9 million in cash, cash equivalents, and investments in marketable securities and $239.9 million in indebtedness, including $215.0 million in outstanding convertible subordinated notes due September 2012. On February 24, 2012, we entered into an agreement whereby we received an aggregate cash payment of $124.0 million in exchange for the right to receive all royalty payments arising from future worldwide net sales of CIMZIA^® and MIRCERA^® from and after January 1, 2012 under our license, manufacturing and supply agreements with UCB Pharma (UCB) and F. Hoffmann-La Roche Ltd and Hoffmann-La Roche Inc. (Roche), respectively. Additionally, we incurred approximately $4.5 million in transaction costs. We plan to use the net payments from this agreement to in part repay the convertible subordinated notes due September 28, 2012 (see Note 14).

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 AL, Corporation (Nektar AL), Nektar Therapeutics (India) Private Limited, Nektar Therapeutics UK, Ltd. (Nektar UK) and Aerogen, Inc. All intercompany accounts and transactions have been eliminated in consolidation. The merger of Nektar AL, an Alabama corporation, with and into its parent corporation, Nektar Therapeutics, was made effective July 31, 2009. As of the effective date, the separate existence of Nektar AL ceased, and all rights, privileges, powers and franchises of Nektar AL are vested in Nektar Therapeutics, the surviving corporation. On December 2, 2010, we completed the dissolution of Aerogen, Inc. and all remaining assets were transferred to Nektar Therapeutics.

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 loss in the stockholders' equity section of the balance sheet. To date, such cumulative translation adjustments have not been material to our consolidated financial position. Aggregate gross foreign currency transaction gains (losses) recorded in operations for the years ended December 31, 2011, 2010, and 2009 were not material.

The preparation of 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 financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ materially from those estimates. On an ongoing basis, we evaluate our estimates, including those related to deferred revenue recognition periods, inventories, the impairment of investments, the impairment of goodwill and long-lived assets, restructuring and contingencies, stock-based compensation, and litigation, amongst others. 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.

Reclassifications

Certain items previously reported in specific financial statement captions have been reclassified to conform to the current period presentation. Such reclassifications do not impact previously reported total revenue, operating loss or net loss or 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 to be cash equivalents. 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 investments is based primarily on the reported fair values in our period-end brokerage statements. We independently validate these fair values using available market quotes and other information. Investments in securities with maturities of less than one year, or where management's intent is to use the investments to fund current operations or to make them available for current operations, are classified as short-term investments

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.

The carrying value of cash, cash equivalents, and investments approximates fair value and is based on quoted market prices.

Accounts Receivable and Significant Customer Concentrations

Our customers are primarily pharmaceutical and biotechnology companies that are located in the U.S. and Europe. Our accounts receivable balance contains billed and unbilled trade receivables from product sales and royalties, as well as time and materials based billings from collaborative research and development agreements. 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' payment histories and associated credit risk. We have not experienced significant credit losses from our accounts receivable. At December 31, 2011, four different customers represented 26%, 20%, 19% and 17%, respectively, of our accounts receivable. At December 31, 2010, two different customers represented 66% and 21%, respectively, of our accounts receivable.

Inventory and Significant Supplier Concentrations

Inventory is generally manufactured upon receipt of firm purchase orders from our licensing partners. Inventory includes direct materials, direct labor, and manufacturing overhead and is determined on a first-in, first-out basis. Inventory is stated at the lower of cost or market and is net of reserves determined using specific identification plus an estimated reserve for potential defective or excess inventory based on historical experience or projected usage. Supplies inventory related to research and development activities are 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 regulatory requirements. In certain cases, we rely on single sources of supply. Consequently, in the event that supplies are delayed or interrupted for any reason, our ability to develop and produce our products could be impaired, which could have a material adverse effect on our business, financial condition and results of operations.

Property and Equipment

Property 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 seven years. Leasehold improvements and buildings are depreciated using the straight-line method over the shorter of the estimated useful life or the remaining term of the lease.

We periodically review our property and equipment for recoverability whenever events or changes in circumstances indicate that the carrying value may not be recoverable. Generally, an impairment loss would be recognized if the carrying amount of an asset exceeds the sum of the discounted cash flows expected to result from the use and eventual disposal of the asset (see Note 10).

Goodwill

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 test for impairment in the fourth quarter of each year using an October 1 measurement date, as well as at other times when impairment indicators exist or when events occur or circumstances change that would indicate the carrying amount may not be fully recoverable.

We are organized in one reporting unit and have evaluated the goodwill for the Company as a whole. Goodwill is tested for impairment using a two-step approach. The first step is to compare the fair value of our net assets, including assigned goodwill, to the book value of our net assets, including assigned goodwill. If the fair value is greater than our net book value, the assigned goodwill is not considered impaired. If the fair value is less than our net book value, we perform a second step to measure the amount of the impairment, if any. The second step would be to compare the book value of our assigned goodwill to the implied fair value of our goodwill. We did not recognize any goodwill-related impairment charges during 2011, 2010, or 2009.

Revenue Recognition

We enter into arrangements with pharmaceutical and biotechnology partners that may involve multiple deliverables. Our arrangements may contain one or more of the following elements: upfront fees, contract research and development, milestone payments, manufacturing and supply, royalties, and license fees. Each deliverable in the arrangement is evaluated to determine whether it meets the criteria to be accounted for as a separate unit of accounting or whether it should be combined with other deliverables. Revenue is recognized separately for each element.

On January 1, 2011, we adopted on a prospective basis Accounting Standards Update (ASU) 2009-13, which amends the criteria to identify separate units of accounting within Subtopic 605-25, "Revenue Recognition-Multiple-Element Arrangements." The adoption of the standard did not impact our financial position or results of operations as of and for the year ended December 31, 2011 as we did not enter into or materially modify any multiple-element arrangements during that period. However, the adoption of this standard may result in revenue recognition patterns for future agreements that are materially different from those recognized for our existing multiple-element arrangements.

Product sales

Product sales are primarily derived from cost-plus and fixed price manufacturing and supply agreements with our collaboration partners and revenue is recognized when there is persuasive evidence that an arrangement exists, delivery has occurred, the price is fixed or determinable, and collection is reasonably assured. We have not experienced any significant returns from our customers.

Royalty revenues

Generally, we are entitled to royalties from our partners based on their net sales of approved drugs. We recognize royalty revenue when the cash is received or when the royalty amount to be received is estimable and collection is reasonably assured.

License, collaboration and other

Upfront fees received for license and collaborative agreements entered into prior to January 1, 2011 are recognized ratably over our expected performance period under each respective arrangement. Management makes its best estimate of the period over which we expect to fulfill our performance obligations, which may include technology transfer assistance, clinical development activities, and manufacturing activities from development through the commercialization of the product. Given the uncertainties of these collaborative arrangements, significant judgment is required to determine the duration of the performance period.

On January 1, 2011, we elected to prospectively adopt ASU 2010-17, "Milestone Method of Revenue Recognition". Under the milestone method, 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 more 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 on either 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 and approvals for drug candidates. Given the challenges inherent in developing and obtaining approval for pharmaceutical and biologic products, there was substantial uncertainty whether any such milestones would be achieved at the time these licensing and collaboration agreements were entered into. 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 development milestones to be substantive and, accordingly, we expect to recognize as revenue future payments received from such milestones as each milestone is achieved. This policy election may result in revenue recognition patterns for future milestones that are materially different from those recognized for milestones received in the periods prior to adoption during which milestones were deferred and recognized ratably over the period of time from the achievement of the milestone to the estimated date when the next milestone will be achieved. During the year ended December 31, 2011, we achieved two development milestones totaling $4.5 million from two of our collaboration agreements. Under the milestone method of revenue recognition, these substantive milestones were recognized in their entirety upon achievement in the year ended December 31, 2011, whereas under our previous milestone revenue recognition policy, we would have recognized approximately $1.5 million related to such amounts during this period. As a result, in the year ended December 31, 2011, this change in accounting policy resulted in increased revenues and a corresponding decrease to net loss of approximately $3.0 million, or $0.03 per share.

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 expect to recognize the payments as revenue when earned under the applicable contract, 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 will recognize such sales-based payments upon achievement of such sales volumes, provided that collection is reasonably assured.

Shipping and Handling Costs

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

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), in which employees may purchase our common stock at a discount to the market price.

We use the Black-Scholes option valuation model for the respective grant to determine the estimated fair value of the option or RSU award 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. 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. 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 that is ultimately expected to vest on a straight line basis over the requisite service periods in our Consolidated Statements of Operations. Stock-based compensation expense for purchases under the ESPP are recognized based on the estimated fair value of the common stock during each offering period and the percentage of the purchase discount. Expense amounts are allocated among inventory, 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.

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.

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.

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, the net loss available to common stockholders is equal to the reported net loss. Basic and diluted net loss per share are the same due to our historical net losses and the requirement to exclude potentially dilutive securities which would have an anti-dilutive effect on net loss per share. The weighted average of these potentially dilutive securities has been excluded from the diluted net loss per share calculation and is as follows (in thousands):


	Year Ended December 31,
	2011		2010		2009
Convertible subordinated notes		9,989		9,989		9,989
Stock options		11,338		9,338		10,653

Total		21,327		19,327		20,642

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 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 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 loss is comprised of net loss, gains and losses from the foreign currency translation of the assets and liabilities of our India subsidiary, and unrealized gains and losses on investments.

Recent Accounting Pronouncements

In September 2011, the Financial Accounting Standards Board issued new accounting guidance intended to simplify goodwill impairment testing. Entities will be allowed to perform a qualitative assessment of goodwill impairment to determine whether a quantitative assessment is necessary. This guidance is effective for our interim and annual periods beginning January 1, 2012. We do not believe the adoption of this guidance will have a material impact on our consolidated financial statements.

Consolidated Statements of Stockholders' Equity (Parenthetical) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011
Net of issuance costs	$ 617
Common Stock
Net of issuance costs	617
Capital in Excess of Par Value
Net of issuance costs	$ 617

Commitments and Contingencies	12 Months Ended
Commitments and Contingencies	Dec. 31, 2011
Commitments and Contingencies [Abstract]
Commitments and Contingencies	Note 7 — Commitments and Contingencies *Royalty Expense* We have third party licenses that require us to pay royalties based on our shipment of certain products and/or on our receipt of royalty payments under our collaboration agreements. Royalty expense, which is reflected in cost of goods sold in our Consolidated Statements of Operations, was approximately $1.8 million, $2.2 million, and $3.9 million for the years ended December 31, 2011, 2010, and 2009, respectively. The overall maximum amount of these obligations is based upon sales of the applicable products and cannot be reasonably estimated. *Other 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, 2011, these commitments were approximately $10.1 million, all of which were expected to be paid in 2012. *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 operations of that period or on our cash flows and liquidity. On November 18, 2009, the Research Foundation of the State University of New York (SUNY) filed an action against Nektar in the United States District Court for the Northern District of New York. SUNY seeks to recover amounts it alleges it is owed pursuant to a technology licensing contract between Nektar and SUNY. We dispute SUNY's claims. Discovery in the matter is continuing and a "trial ready" date has been set for September 1, 2012. We believe that SUNY's claims are without merit. No reasonable estimate of the possible loss or range of loss can be made at this time and no liabilities have been recorded for this matter on our Consolidated Balance Sheets as of December 31, 2011 or 2010. *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, we generally agree to defend, indemnify and hold harmless our partners from and against third party liabilities arising out of the agreement, including product liability (with respect to our activities) and infringement of intellectual property to the extent the intellectual property is developed by us and licensed to our partners. The term of these indemnification obligations is generally perpetual any time after execution of the agreement. There is generally no limitation on the potential amount of future payments we could be required to make under these indemnification obligations. As part of our pulmonary asset sale to Novartis that closed on December 31, 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 were determined that we breached any of the representations and warranties or covenants and agreements made by us in the transaction documents, we could incur an indemnification liability depending on the timing, nature, and amount of any such claims. To date we have not incurred costs to defend lawsuits or settle claims related to these indemnification obligations. If any of our indemnification obligations is triggered, we may incur substantial liabilities. Because the obligated amount under these agreements is not explicitly stated, the overall maximum amount of the obligations cannot be reasonably estimated. No liabilities have been recorded for these obligations on our Consolidated Balance Sheets as of December 31, 2011 or 2010. *Indemnification of Underwriters and Initial Purchasers of our Securities* In connection with our sale of equity and convertible 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. The term of these indemnification obligations is generally perpetual. There is no limitation on the potential amount of future payments we could be required to make under these indemnification obligations. We have never incurred costs to defend lawsuits or settle claims related to these indemnification obligations. If any of our indemnification obligations are triggered, however, we may incur substantial liabilities. Because the obligated amount of this agreement is not explicitly stated, the overall maximum amount of the obligations cannot be reasonably estimated. Historically, we have not been obligated to make significant payments for these obligations, and no liabilities have been recorded for these obligations in our Consolidated Balance Sheets as of December 31, 2011 or 2010. *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 $500,000 per incident for securities related claims and $250,000 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. Because the obligated amount of this agreement is not explicitly stated, the overall maximum amount of the obligations cannot be reasonably estimated. Historically, we have not been obligated to make significant payments for these obligations, and no liabilities have been recorded for these obligations in our Consolidated Balance Sheets as of December 31, 2011 or 2010.

Impairment of Long Lived Assets	12 Months Ended
Impairment of Long Lived Assets	Dec. 31, 2011
Impairment of Long Lived Assets [Abstract]
Impairment of Long Lived Assets	Note 10 — Impairment of Long Lived Assets During the year ended December 31, 2010, we recorded a charge for the impairment of long-lived assets of $12.6 million. We did not record any such charge in 2009 or 2011. On November 29, 2010, we ceased use of the San Carlos facility as a result of our relocation to the Mission Bay Facility. The remaining assets at the San Carlos location consist of the building capital lease and related leasehold improvements. We have subleased a portion of the San Carlos building and are currently seeking one or more subtenants for the remaining space through the lease termination date. As a result of our relocation, we performed an impairment analysis on these assets. We concluded that the carrying values of the building and leasehold improvements exceeded their fair values based on a probability-weighted discounted cash flow model of the future estimated net sublease income and recorded an impairment loss of $12.6 million. As of December 31, 2011, the remaining net book value of these assets is $1.7 million.

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2011
Subsequent Events [Abstract]
Subsequent Events	Note 14 — Subsequent Events *Sale of CIMZIA^® and MIRCERA^® 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, on February 29, 2012, we sold, and RPI purchased, our right to receive royalty payments (the "Royalty Entitlement") arising in respect of worldwide net sales, from and after January 1, 2012, of (a) CIMZIA^®, under Nektar's license, manufacturing and supply agreement with UCB, and (b) MIRCERA^®, under Nektar's license, manufacturing and supply agreement with Roche. We received an aggregate cash purchase price for the Royalty Entitlement of $124.0 million. Additionally, we incurred approximately $4.5 million in transaction costs. Pursuant to the Purchase and Sale Agreement, we are required to pay to RPI (a) $3.0 million if certain worldwide net sales thresholds of MIRCERA^® for the 12 month period ending on December 31, 2012 are not achieved and (b) up to an additional $7.0 million if certain worldwide net sales thresholds of MIRCERA^® for the 12 month period ending on December 31, 2013 are not achieved. 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. In particular, if we breach our obligations under the Purchase and Sale Agreement, we may be required to pay damages to RPI that could potentially exceed the purchase price. Except as described above, RPI is entitled only to the future royalty payments arising from sales of CIMZIA^® and MIRCERA^®. However, we have significant continuing involvement in the generation of these future royalty payments through our ongoing manufacturing and supply obligations to UCB and Roche. As a result, we will record a long-term liability on our consolidated balance sheet equal to the fair value of the Purchase and Sale Agreement, which approximates the up-front purchase price, and will amortize the liability using the effective interest rate method over its estimated life. As a result of this liability accounting, even though the royalties from UCB and Roche will be remitted directly to RPI, we will continue to record revenue for these royalties. The model used to estimate the fair value of the rights sold to RPI requires us to make estimates regarding, among other things, the assumptions market participants would make regarding the timing and probability of achieving the royalties, as well as the appropriate discount rates. The effective interest rate under the agreement is estimated to be approximately 17%. During the years ended December 31, 2011, 2010, and 2009, we recognized $8.3 million, $5.4 million, and $2.7 million, respectively, in aggregate royalties from net sales of MIRCERA^® and CIMZIA^®. We intend to use the net proceeds of this agreement to in part repay the $215.0 million aggregate amount of outstanding 3.25% Convertible Subordinated Notes due September 28, 2012. *Roche MIRCERA^® Manufacturing Agreement* On February 28, 2012, we entered into a toll-manufacturing agreement with Roche under which we will manufacture the proprietary PEGylation material for MIRCERA^®. Roche entered into the toll-manufacturing agreement with the objective of establishing us as a secondary back-up source on a non-exclusive basis. Under the terms of the toll-manufacturing agreement, Roche agreed to pay us an up-front payment of $5.0 million plus a total of up to $22.0 million in performance-based milestone payments upon our achievement of certain manufacturing readiness, validation and production milestones which are scheduled to be completed by the end of January 2013. There is a risk that we will not meet one or more of the milestones on a timely basis or at all. Roche will also pay us additional consideration for any future orders of the PEGylation materials for MIRCERA^® beyond the initial quantities scheduled to be manufactured and supplied in 2012. Roche may terminate the toll-manufacturing agreement due to an uncured material default by us or for convenience under certain circumstances and subject to certain financial obligations.

Organization and Summary of Significant Accounting Policies (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2011 years	Dec. 31, 2010
Finite-Lived Intangible Assets [Line Items]
Outstanding convertible subordinated notes	$ 214,955,000
Organization and Summary of Significant Accounting Policies (Textual) [Abstract]
Cash and cash equivalents, and Investment in marketable securities	414,900,000
Indebtedness	239,900,000
Maximum maturity term of investments in marketable securities to be considered as cash equivalents	3 months
Maturity term of investments considered as short term	*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 to be cash equivalents. 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 investments is based primarily on the reported fair values in our period-end brokerage statements. We independently validate these fair values using available market quotes and other information. Investments in securities with maturities of less than one year, or where management's intent is to use the investments to fund current operations or to make them available for current operations, are classified as short-term investments 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. The carrying value of cash, cash equivalents, and investments approximates fair value and is based on quoted market prices.
Number of customers accounted for major accounts receivable	4	2
Percentage of accounts receivable customers one	26.00%	66.00%
Percentage of accounts receivable customers two	20.00%	21.00%
Percentage of accounts receivable customers three	19.00%
Percentage of accounts receivable customers four	17.00%
Estimated useful lives, minimum	3
Estimated useful lives, maximum	7
Minimum percentage of amount realized upon ultimate settlement	50.00%
Allowance for doubtful accounts
Development milestones payments received upon achievement	4,500,000
Number of collaboration agreements from which development milestones achieved	2
Recognized revenue under previous milestone revenue recognition policy	1,500,000
Increase in revenue under milestone method of revenue recognition	3,000,000
Increase in per share under milestone method of revenue recognition	$ 0.03
Purchase and Sale Agreement with RPI [Member]
Finite-Lived Intangible Assets [Line Items]
Proceeds from sale of royalty rights	124,000,000
Structuring transaction costs	$ 4,500,000

Cash, Cash Equivalents, and Available-For-Sale Investments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Cash, cash equivalents, and available-for-sale investments
Cash and cash equivalents	$ 15,312	$ 17,755	$ 49,597	$ 155,584
Short-term investments	225,856	298,177
Long-term investments	173,768
Total cash, cash equivalents, and available-for-sale investments	$ 414,936	$ 315,932

Cash, Cash Equivalents, and Available-For-Sale Investments (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008
Schedule of Available-for-sale Securities [Line Items]
Cash and money market funds	$ 15,312	$ 17,755	$ 49,597	$ 155,584
Cash, cash equivalents, and available-for-sale investments	414,936	315,932
Corporate notes and bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, fair value	344,427	190,527
U.S. corporate commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, fair value	9,464	82,361
Obligations of U.S. government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, fair value	44,230	25,289
Obligations of U.S. states and municipalities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, fair value	$ 1,503	$ 0

Cash, Cash Equivalents, and Available-For-Sale Investments (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Available-for-sale Securities [Abstract]
Less than one year	$ 213,386	$ 298,177
Greater than one year but less than two years	186,238
Total available-for-sale investments	$ 399,624	$ 298,177

Cash, Cash Equivalents, and Available-For-Sale Investments (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Fair value assets measured on recurring basis
Cash, cash equivalents, and available-for-sale investments	$ 414,936	$ 315,932
U.S. corporate commercial paper [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	9,464	82,361
Corporate notes and bonds [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	344,427	190,527
Obligations of U.S. government agencies [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	44,230	25,289
Obligations of U.S. states and municipalities [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	1,503	0
Recurring [Member]
Fair value assets measured on recurring basis
Money market funds	13,950	16,028
Cash equivalents and available-for-sale investments, fair value	413,574	314,205
Cash	1,362	1,727
Cash, cash equivalents, and available-for-sale investments	414,936	315,932
Recurring [Member] \| Level 1 [Member]
Fair value assets measured on recurring basis
Money market funds	13,950	16,028
Cash equivalents and available-for-sale investments, fair value	13,950	16,028
Recurring [Member] \| Level 2 [Member]
Fair value assets measured on recurring basis
Money market funds	0	0
Cash equivalents and available-for-sale investments, fair value	399,624	298,177
Recurring [Member] \| Level 3 [Member]
Fair value assets measured on recurring basis
Money market funds	0	0
Cash equivalents and available-for-sale investments, fair value	0	0
Recurring [Member] \| U.S. corporate commercial paper [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	9,464	82,361
Recurring [Member] \| U.S. corporate commercial paper [Member] \| Level 1 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	0	0
Recurring [Member] \| U.S. corporate commercial paper [Member] \| Level 2 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	9,464	82,361
Recurring [Member] \| U.S. corporate commercial paper [Member] \| Level 3 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	0	0
Recurring [Member] \| Corporate notes and bonds [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	344,427	190,527
Recurring [Member] \| Corporate notes and bonds [Member] \| Level 1 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	0	0
Recurring [Member] \| Corporate notes and bonds [Member] \| Level 2 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	344,427	190,527
Recurring [Member] \| Corporate notes and bonds [Member] \| Level 3 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	0	0
Recurring [Member] \| Obligations of U.S. government agencies [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	44,230	25,289
Recurring [Member] \| Obligations of U.S. government agencies [Member] \| Level 1 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	0	0
Recurring [Member] \| Obligations of U.S. government agencies [Member] \| Level 2 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	44,230	25,289
Recurring [Member] \| Obligations of U.S. government agencies [Member] \| Level 3 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	0	0
Recurring [Member] \| Obligations of U.S. states and municipalities [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	1,503
Recurring [Member] \| Obligations of U.S. states and municipalities [Member] \| Level 1 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	0
Recurring [Member] \| Obligations of U.S. states and municipalities [Member] \| Level 2 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	1,503
Recurring [Member] \| Obligations of U.S. states and municipalities [Member] \| Level 3 [Member]
Fair value assets measured on recurring basis
Available-for-sale securities, fair value	$ 0

Inventory (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Inventory
Raw materials	$ 9,754	$ 6,101
Work-in-process	1,219	0
Finished goods	1,683	1,165
Inventory	$ 12,656	$ 7,266

Property and Equipment (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Property and equipment
Depreciable property and equipment at cost	$ 139,063	$ 141,210
Less: accumulated depreciation	(62,237)	(53,994)
Depreciable property and equipment, net	76,826	87,216
Construction-in-progress	1,750	2,557
Property and equipment, net	78,576	89,773
Building and leasehold improvements [Member]
Property and equipment
Depreciable property and equipment at cost	72,473	73,150
Laboratory equipment [Member]
Property and equipment
Depreciable property and equipment at cost	33,705	31,871
Manufacturing equipment [Member]
Property and equipment
Depreciable property and equipment at cost	12,135	13,386
Furniture, fixtures and other equipment [Member]
Property and equipment
Depreciable property and equipment at cost	$ 20,750	$ 22,803

Property and Equipment (Details Textual) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
	Nov. 30, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Property and Equipment (Textual) [Abstract]
Depreciation expense		$ 15.0	$ 14.8	$ 12.7
Impairment charge on capital lease	$ 12.6

Convertible Subordinated Notes (Details) (3.25% Notes due September 2012 [Member], USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2011
3.25% Notes due September 2012 [Member]
Outstanding balance of convertible subordinated notes
Convertible subordinated notes outstanding	$ 214,955	$ 214,955
Semi-Annual Interest Payment Dates	March 28, September 28

Convertible Subordinated Notes (Details Textual) (USD $)	12 Months Ended
	Dec. 31, 2011
Convertible Subordinated Notes (Textual) [Abstract]
Notes conversion rate	46.4727
Principal amount of convertible Note	$ 1,000
Conversion Price	$ 21.52
Debt instrument convertible terms of redemption	We may redeem the Notes in whole or in part for cash at a redemption price equal to 100% of the principal amount of the Notes plus any accrued but unpaid interest if the closing price of the common stock has exceeded 150% of the conversion price for at least 20 days in any consecutive 30 day trading period.
Percentage of principal amount	100.00%
Percentage of conversion price	150.00%
Closing price of common stock exceeding conversion price period	20 days
Consecutive trading period	30 days
3.25% Notes due September 2012 [Member]
Debt Instrument [Line Items]
Percentage interest rate of convertible subordinated notes due	3.25%

Leases (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Gross carrying value by major asset class and accumulated depreciation
Total assets recorded under capital leases	$ 2,312	$ 2,312
Less: accumulated depreciation	(464)	(54)
Net assets recorded under capital leases	1,848	2,258
Building and leasehold improvements [Member]
Gross carrying value by major asset class and accumulated depreciation
Total assets recorded under capital leases	2,117	2,117
Furniture, fixtures and other equipment [Member]
Gross carrying value by major asset class and accumulated depreciation
Total assets recorded under capital leases	$ 195	$ 195

Leases (Details 1) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Future minimum payments for capital leases
2012	$ 5,028
2013	5,129
2014	5,191
2015	5,280
2016	4,034
Total minimum payments required	24,662
Less: amount representing interest	(7,648)
Present value of future minimum lease payments	17,014
Less: current portion	(2,432)
Non-current portion	$ 14,582	$ 17,014

Leases (Details 2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Future minimum lease payments under the Sublease
2012	$ 480
2013	200
2014	1,509
2015	3,667
2016	3,777
2017 and thereafter	12,367
Total future minimum lease payments	$ 22,000

Leases (Details Textual) (USD $)	1 Months Ended	12 Months Ended
Leases (Details Textual) (USD $)	Nov. 30, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 28, 2011 sqft	Sep. 30, 2009 sqft
Leases (Textual) [Abstract]
Percentage ceiling on rent increase, annually, capital lease		3.00%
San Carlos facility capital leases termination date		Oct. 05, 2016
Impairment charge on capital lease	$ 12,600,000
Operating sublease						102,283
Additional area included in operating sublease after amendment					24,002
Operating Sublease term commenced start date		August 1, 2010
Operating Sublease term commenced period		114 months
Operating Sublease term commenced end date		January 31, 2020
Initial monthly base rent per square foot, operating lease		2.95
Operating lease expense per month after amendment		40,000
Final monthly base rent per square foot, operating lease		3.42
Rent expense for operating leases		$ 2,400,000	$ 2,200,000	$ 700,000

Commitments and Contingencies (Details) (USD $)	12 Months Ended
Commitments and Contingencies (Details) (USD $)	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Commitments and Contingencies (Textual) [Abstract]
Royalty expense	$ 1,800,000	$ 2,200,000	$ 3,900,000
Purchase commitments related to contract manufacturing, clinical development and certain other items	10,100,000
Securities related claims [Member]
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	500,000
Non-securities related claims [Member]
Loss Contingencies [Line Items]
Obligations under Director and Officer Indemnifications per incident	$ 250,000

Stockholders' Equity (Details) In Thousands, unless otherwise specified	Dec. 31, 2011
Class of Stock [Line Items]
Total	35,377
Convertible subordinated notes [Member]
Class of Stock [Line Items]
Total	9,989
Equity compensation plans [Member]
Class of Stock [Line Items]
Total	25,388

Stockholders' Equity (Details1) (USD $) In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2011
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	17,182
Weighted-Average Exercise Price of Outstanding Options	$ 9.29
Number of Securities Remaining Available for Issuance under Equity Compensation Plans (Excluding Securities Reflected in Column	8,206
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	10,051
Weighted-Average Exercise Price of Outstanding Options	$ 8.98
Number of Securities Remaining Available for Issuance under Equity Compensation Plans (Excluding Securities Reflected in Column	7,600
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	7,131
Weighted-Average Exercise Price of Outstanding Options	$ 9.73
Number of Securities Remaining Available for Issuance under Equity Compensation Plans (Excluding Securities Reflected in Column	606

Stockholders' Equity (Details Textual) (USD $) In Millions, except Share data, unless otherwise specified						1 Months Ended
	Dec. 31, 2011	Jan. 31, 2011	Dec. 31, 2010	Dec. 31, 2011 Preferred Stock [Member]	Dec. 31, 2011 Series A Junior Participating Preferred Stock [Member]	Jan. 31, 2011 Common Stock	Jan. 24, 2011 Common Stock
Preferred Stock, Number of Shares, Par Value and Other Disclosures
Preferred stock, shares authorized	10,000,000		10,000,000	10,000,000	3,100,000
Preferred stock, par value	$ 0.0001		$ 0.0001	$ 0.0001
Common Stock, Number of Shares, Par Value and Other Disclosures
Common stock, shares issued	114,485,000	19,000,000	94,517,000				19,000,000
Proceeds from sale of common stock						$ 220.4
Stock offering expenses						$ 0.6

Stockholders' Equity (Details Textual 1) (Share Purchase Rights Plan [Member], USD $)	12 Months Ended
	Dec. 31, 2011
Share Purchase Rights Plan [Member]
Stockholders Equity (Textual 1) [Abstract]
Title of Rights	preferred share purchase right
Number of Series A Preferred Shares called by one Right, in shares	0.01
Exercise price on one Right	$ 225.00
Reason for issuing rights	anti-takeover effects

Stockholders' Equity (Details Textual 2) (USD $)	12 Months Ended
Stockholders' Equity (Details Textual 2) (USD $)	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stockholders Equity (Textual 2) [Abstract]
Minimum voting power percentage for accelerated vesting period	10.00%
RSU awards par value	$ 0.0001	$ 0.0001
Restricted stock units award depletion ratio	1:1.5
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	$ 3,000
Compensation expense in connection with 401(k) plan	$ 900,000	$ 1,000,000	$ 800,000
Severance payment period for executives	12 months
Cash severance payment for chief executive officer	24 months base salary plus annual target incentive pay
Severance payment period for employees	6 months
2008 Equity Incentive Plan [Member]
Stockholders Equity (Textual 2) [Abstract]
Number of common stock available for stock options grants	9,000,000
Share-based compensation plan's share limit reduction for every one restricted stock unit granted	1.5
Maximum term of stock options under equity incentive plans	8 years
Minimum voting power percentage for accelerated vesting period	10.00%
Maximum term of incentive stock option for holders of more than ten percent of voting right	5 years
Exercise price of stock options granted	100.00%
Exercise price of stock options granted for holders of more than ten percent of voting right	110.00%
2000 Equity Incentive Plan [Member]
Stockholders Equity (Textual 2) [Abstract]
Maximum term of stock options under equity incentive plans	8 years
Maximum term of incentive stock option for holders of more than ten percent of voting right	5 years
Exercise price of stock options granted	100.00%
Exercise price of stock options granted for holders of more than ten percent of voting right	110.00%
2000 Non-Officer Equity Incentive Plan [Member]
Stockholders Equity (Textual 2) [Abstract]
Maximum term of stock options under equity incentive plans	8 years
Restricted Stock Units [Member]
Stockholders Equity (Textual 2) [Abstract]
RSU awards par value	$ 0.01
Employee Stock Purchase Plan [Member]
Stockholders Equity (Textual 2) [Abstract]
Common stock, shares authorized	1,500,000
Percentage of purchase price of stock	85.00%

License and Collaboration Agreements (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
License, collaboration, and other revenue
License, collaboration and other revenue	$ 6,614	$ 16,846	$ 6,323	$ 6,506	$ 32,615	$ 30,695	$ 31,409	$ 29,653	$ 36,289	$ 124,372	$ 36,643
Baxter Healthcare [Member] \| Hemophilia [Member]
License, collaboration, and other revenue
License, collaboration and other revenue									5,646	1,701	2,055
F Hoffmann La Roche [Member] \| PEGASYS [Member]
License, collaboration, and other revenue
License, collaboration and other revenue									5,131	5,131	214
Amgen Inc [Member] \| Neulasta [Member]
License, collaboration, and other revenue
License, collaboration and other revenue									5,000	833
Bayer Healthcare L L C [Member] \| BAY41-6551 (Amikacin Inhale) [Member]
License, collaboration, and other revenue
License, collaboration and other revenue									2,992	3,300	4,928
AstraZeneca AB [Member] \| NKTR-118 and NKTR-119 [Member]
License, collaboration, and other revenue
License, collaboration and other revenue									2,496	107,854	25,073
Other [Member]
License, collaboration, and other revenue
License, collaboration and other revenue									$ 15,024	$ 5,553	$ 4,373

Impairment of Long Lived Assets (Details) (USD $)	3 Months Ended	12 Months Ended
Impairment of Long Lived Assets (Details) (USD $)	Dec. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Impairment of Long Lived Assets (Textual) [Abstract]
Impairment of long-lived assets	$ 12,576,000	$ 0	$ 12,576,000	$ 0
Method for determining fair value		Probability-weighted discounted cash flow model of the future estimated net sublease income
Net book value of assets		$ 1,700,000

Stock-Based Compensation (Details 1)	12 Months Ended
Stock-Based Compensation (Details 1)	Dec. 31, 2011 years	Dec. 31, 2010 years	Dec. 31, 2009 years
Stock options [Member]
Black-Scholes option-pricing model assumptions used to calculate the fair value of employee stock options and ESPP purchases
Average risk-free interest rate	1.60%	1.80%	1.60%
Dividend yield	0.00%	0.00%	0.00%
Volatility factor	63.80%	62.70%	61.00%
Weighted average expected life	4.9	4.9	4.9
Employee Stock Purchase Plan [Member]
Black-Scholes option-pricing model assumptions used to calculate the fair value of employee stock options and ESPP purchases
Average risk-free interest rate	0.10%	0.20%	0.30%
Dividend yield	0.00%	0.00%	0.00%
Volatility factor	53.60%	47.80%	82.40%
Weighted average expected life	0.5	0.5	0.5

Income Taxes (Details 3) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Deferred tax assets:
Net operating loss carryforwards	$ 342,128	$ 318,257
Research and other credits	51,125	49,657
Capitalized research expenses	9,514	5,797
Deferred revenue	48,732	31,411
Property and equipment	8,081	7,654
Reserve and accruals	8,083	5,732
Stock-based compensation	32,268	28,157
Other	3,895	4,275
Deferred tax assets before valuation allowance	503,826	450,940
Valuation allowance for deferred tax assets	(503,689)	(450,781)
Total deferred tax assets	137	159
Deferred tax liabilities:
Property and equipment	(75)	0
Total deferred tax liabilities	(75)	0
Net deferred tax assets	$ 62	$ 159

Income Taxes (Details Textual) (USD $)	12 Months Ended
Income Taxes (Details Textual) (USD $)	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Jan. 31, 2011
Income Taxes (Textual) [Abstract]
Statutory income tax rate	35.00%
Increase in valuation allowance	$ 52,900,000	$ 8,300,000
Valuation allowance related to stock-based compensation and exercises prior to the implementation of ASC 515 and 718	35,600,000	35,600,000
Deferred U.S. income taxes	0	0	0
Common stock, shares sold	114,485,000	94,517,000		19,000,000
Federal orphan drug credits	13,000,000
Unrecognized tax benefits, period increase (decrease) reasonable period of change	next twelve months
Interest or penalties related to income tax	0	0
Federal [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforward for income tax purposes	874,000,000
Income tax research credits	23,800,000
State [Member]
Income Tax Contingency [Line Items]
Net operating loss carryforward for income tax purposes	584,800,000
Income tax research credits	$ 14,000,000

Segment Reporting (Details Textual)	12 Months Ended
Segment Reporting (Details Textual)	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Reporting (Textual) [Abstract]
Number of operating business segment	1
Number of components within business segment	2
Revenue derived from number of partners	2	1	2
AstraZeneca AB [Member]
Revenue, Major Customer [Line Items]
Percentage revenue from clients		68.00%	35.00%
UCB Pharma [Member]
Revenue, Major Customer [Line Items]
Percentage revenue from clients	27.00%		17.00%
Roche [Member]
Revenue, Major Customer [Line Items]
Percentage revenue from clients	16.00%