License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 2,535	$ 1,064,246	$ 6,739	$ 1,077,973
Bristol-Myers Squibb | NKTR-214
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	1,059,768	0	1,059,768
Eli Lilly and Company | NKTR-358
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,200	3,052	3,700	5,406
Baxalta Incorporated/Takeda | ADYNOVATE
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	58	18	78	10,028
Amgen, Inc. | Neulasta
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250	2,500	2,500
Other
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 27	$ 158	$ 461	$ 271