License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 1,631	$ 3,121	$ 55,421	$ 9,860
Bristol-Myers Squibb Company | Bempegaldesleukin
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	0	50,000	0
Eli Lilly and Company | NKTR-358
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	1,500	1,259	5,200
Amgen, Inc. | Neulasta
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250	3,750	3,750
Other
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 381	$ 371	$ 412	$ 910