License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 27,515	$ 4,204
Bristol-Myers Squibb Company | Bempegaldesleukin
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	25,000	0
Eli Lilly and Company | NKTR-358
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,259	2,500
Amgen, Inc. | Neulasta
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250
Other
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 6	$ 454