License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 26,275	$ 2,535	$ 53,790	$ 6,739
Bristol-Myers Squibb Company | Bempegaldesleukin
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	25,000	0	50,000	0
Eli Lilly and Company | NKTR-358
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	1,200	1,259	3,700
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	$ 25	$ 85	$ 31	$ 539