License and Collaboration Agreements - Additional Information (Detail) - USD ($)		1 Months Ended							3 Months Ended				9 Months Ended	12 Months Ended
	Sep. 16, 2014	Aug. 31, 2015	Oct. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Nov. 30, 2013	Jun. 30, 2013	Feb. 29, 2012	Mar. 31, 2015	Dec. 31, 2013	Dec. 31, 2010	Dec. 31, 2009	Sep. 30, 2015	Dec. 31, 2007	Jul. 31, 2016	Jul. 31, 2015
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones													$ 128,300,000
Roche [Member] | MIRCERA [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue													6,700,000
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 [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue													1,300,000
Roche [Member] | PEGASYS and MIRCERA [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue													2,900,000
Amgen, Inc. [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments											$ 50,000,000
Deferred revenue													25,400,000
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					$ 19,750,000
Deferred revenue													18,200,000
Potential future development milestones upon acceptance for review of regulatory approval													2,500,000
AstraZeneca AB [Member] | United States [Member]
Deferred Revenue Arrangement [Line Items]
Liability to AZ for DTC advertising payments									$ 10,000,000							$ 5,000,000
Reduction of revenue									(10,000,000)
AstraZeneca AB [Member] | Scenario, Forecast [Member] | United States [Member] | Other Current Liabilities [Member]
Deferred Revenue Arrangement [Line Items]
Liability to AZ for DTC advertising payments															$ 5,000,000
AstraZeneca AB [Member] | MOVANTIK [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments			$ 35,000,000			$ 70,000,000			$ 100,000,000
Deferred revenue													0
Percentage of post approval study costs to repay	33.00%
Maximum potential reduction in royalties	$ 35,000,000
AstraZeneca AB [Member] | MOVANTIK [Member] | European Union [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments		$ 40,000,000
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] | 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]
Contingent payments receivable based on development events regulatory to be pursued and completed solely by others													75,000,000
Bayer Healthcare LLC [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones													50,000,000
Deferred revenue													19,600,000
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
Baxalta Incorporated [Member] | BAX 855 (Hemophilia) [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones													20,000,000
Deferred revenue													0
Development milestones achieved				$ 8,000,000
Baxalta Incorporated [Member] | BAX 855 (Hemophilia) [Member] | United States [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones													10,000,000
Other [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones													51,800,000
Deferred revenue													$ 15,500,000