License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 55,849	$ 16,975	$ 1,097,265
Bristol-Myers Squibb | Bempegaldesleukin
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	50,000	0	1,059,768
Eli Lilly and Company | NKTR-358
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,259	7,019	11,634
Amgen, Inc. | Neulasta
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	4,167	5,000	5,000
Baxalta Incorporated / Takeda | Hemophilia, Including ADYNOVATE and ADYNOVITM
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	346	378	20,328
Other
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 77	$ 4,578	$ 535