License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 1,064,246	$ 4,824	$ 1,077,973	$ 10,916
Bristol-Myers Squibb [Member] | NKTR-214 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,059,768	0	1,059,768	0
Baxalta Incorporated/Shire [Member] | ADYNOVATE [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	18	45	10,028	45
Eli Lilly and Company [Member] | NKTR-358 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	3,052	0	5,406	0
Amgen, Inc. [Member] | Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250	2,500	2,500
AstraZeneca AB [Member] | MOVANTIK and MOVANTIK fixed-dose combination program [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	1,600	0	4,600
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 158	$ 1,929	$ 271	$ 3,771