License and Collaboration Agreements - Additional Information (Detail) - USD ($)					1 Months Ended									3 Months Ended				9 Months Ended	12 Months Ended
	Sep. 21, 2016	May 30, 2016	Mar. 01, 2016	Sep. 16, 2014	Aug. 31, 2016	Apr. 30, 2016	Mar. 31, 2016	Nov. 30, 2015	Aug. 31, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2013	Feb. 29, 2012	Sep. 30, 2016	Dec. 31, 2013	Dec. 31, 2010	Dec. 31, 2009	Sep. 30, 2016	Dec. 31, 2013	Dec. 31, 2007	Jul. 31, 2016	Dec. 31, 2015	Jul. 31, 2015
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones																		$ 147,000,000
Liability for refundable upfront payment														$ 12,500,000				$ 12,500,000				$ 0
ONZEALDTM (NKTR-102) [Member] | Turkey [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of royalty on net sales		15.00%
AstraZeneca-ProStrakan [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of upfront payment, market access milestones, royalties and sales milestones			40.00%
Bristol-Myers Squibb [Member] | NKTR-214 [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of out-of-pocket costs reimbursed by partner	50.00%
License agreement exclusivity expiration date																		Sep. 30, 2018
License agreement exclusivity negotiation period																		3 months
Daiichi Sankyo Europe GmbH [Member] | ONZEALDTM (NKTR-102) [Member]
Deferred Revenue Arrangement [Line Items]
Eligible milestone payments receivable upon achievement of regulatory and commercial milestones		$ 60,000,000
Milestone payments to be received upon first commercial sales		10,000,000
Milestone payment to be received upon first commercial sale after final regulatory approval		25,000,000
Milestone payments to be received upon first achievement of annual net sales target		$ 25,000,000
Liability for refundable upfront payment														12,500,000				$ 12,500,000
Daiichi Sankyo Europe GmbH [Member] | ONZEALDTM (NKTR-102) [Member] | European Territory Except Turkey [Member]
Deferred Revenue Arrangement [Line Items]
Percentage of royalty on net sales		20.00%
Daiichi Sankyo Europe GmbH [Member] | ONZEALDTM (NKTR-102) [Member] | Upfront Payment Arrangement [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments					$ 20,000,000
Non-refundable portion of upfront payment		$ 7,500,000
Revenue recognized from upfront payment																		3,500,000
Deferred revenue														4,000,000				4,000,000
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] | MOVANTIKTM and MOVANTIKTM fixed-dose combination program [Member] | Upfront Payment Arrangement [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]
Received upfront and milestone payments						$ 28,000,000								3,000,000
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%
Contingent payment recognized as revenue							$ 28,000,000
Baxalta Incorporated [Member] | ADYNOVATETM (Hemophilia) [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue														0				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 [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														1,900,000				1,900,000
Amgen, Inc. [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments																$ 50,000,000
Deferred revenue														20,400,000				20,400,000
Bayer Healthcare LLC [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones																		50,000,000
Deferred revenue														18,200,000				18,200,000
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 [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														17,200,000				17,200,000
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														$ 9,400,000				$ 9,400,000