License and Collaboration Agreements - Additional Information (Detail) - USD ($)			1 Months Ended							3 Months Ended				12 Months Ended
	Mar. 01, 2016	Sep. 16, 2014	Mar. 31, 2016	Nov. 30, 2015	Aug. 31, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2013	Feb. 29, 2012	Mar. 31, 2016	Dec. 31, 2013	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2007	Jul. 31, 2016	Dec. 31, 2015	Jul. 31, 2015
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones										$ 112,000,000
AstraZeneca-ProStrakan [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of upfront payment, market access milestones, royalties and sales milestones	40.00%
AstraZeneca AB [Member] | United States [Member]
Deferred Revenue Arrangement [Line Items]
Liability to AZ for DTC advertising payments						$ 10,000,000											$ 5,000,000
Reduction of revenue						(10,000,000)
AstraZeneca AB [Member] | Scenario, Forecast [Member] | Other Current Liabilities [Member] | United States [Member]
Deferred Revenue Arrangement [Line Items]
Liability to AZ for DTC advertising payments															$ 5,000,000
AstraZeneca AB [Member] | MOVANTIKTM (NKTR-118) and MOVANTIKTM fixed-dose combination program (NKTR-119) [Member] | Upfront Payment Arrangement in 2007 [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments													$ 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 payments						$ 100,000,000
Percentage of post approval study costs to repay		33.00%
Maximum potential reduction in royalties		$ 35,000,000
AstraZeneca AB [Member] | MOVANTIK [Member] | United States [Member]
Deferred Revenue Arrangement [Line Items]
Potential reduction in U.S. royalty rate for repayment		2.00%
AstraZeneca AB [Member] | MOVANTIK [Member] | European Union [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments					$ 40,000,000
AstraZeneca AB [Member] | AstraZeneca-ProStrakan [Member]
Deferred Revenue Arrangement [Line Items]
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%
Upfront revenue recognized			28,000,000
Deferred revenue			0							0
Baxalta Incorporated [Member] | ADYNOVATETM (Hemophilia) [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue																$ 0
Development milestones achieved				$ 10,000,000
Baxalta Incorporated [Member] | ADYNOVATETM (Hemophilia) [Member] | European Union [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones										10,000,000
Roche [Member] | MIRCERA [Member]
Deferred Revenue Arrangement [Line Items]
Consideration received for product delivered in 2013											$ 18,600,000
Roche [Member] | MIRCERA [Member] | Performance-based Milestone Payments [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments									$ 22,000,000
Roche [Member] | MIRCERA [Member] | Upfront Payment Arrangement in 2007 [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments									$ 5,000,000
Roche [Member] | PEGASYS and MIRCERA [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue			5,700,000							5,700,000
Amgen, Inc. [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments												$ 50,000,000
Deferred revenue			22,900,000							22,900,000
Bayer Healthcare LLC [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones										50,000,000
Deferred revenue			18,900,000							18,900,000
Payment made to Bayer for cost of Phase 3 clinical trial								$ 10,000,000
Bayer Healthcare LLC [Member] | Performance-based Milestone Payments [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments										30,000,000
Bayer Healthcare LLC [Member] | Upfront Payment Arrangement in 2007 [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments														$ 40,000,000
Ophthotech Corporation [Member] | Fovista [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones										9,500,000
Received upfront and milestone payments							$ 19,800,000
Deferred revenue			17,900,000							17,900,000
Potential future development milestones upon acceptance for review of regulatory approval			2,500,000							2,500,000
Other [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones										45,500,000
Deferred revenue			$ 11,400,000							$ 11,400,000