License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 4,875	$ 131,112	$ 1,082,848	$ 142,028
Bristol-Myers Squibb [Member] | NKTR-214 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	0	1,059,768	0
Baxalta Incorporated/Shire [Member] | ADYNOVATE [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	300	312	10,328	357
Eli Lilly and Company [Member] | NKTR-358 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	3,221	127,553	8,627	127,553
Amgen, Inc. [Member] | Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250	3,750	3,750
AstraZeneca AB [Member] | MOVANTIK and MOVANTIK fixed-dose combination program [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	0	0	4,600
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 104	$ 1,997	$ 375	$ 5,768