License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 16,975	$ 1,097,265	$ 210,965
Collaboration agreements completion date	Dec. 31, 2017
Bristol-Myers Squibb | NKTR-214
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 0	1,059,768	0
Eli Lilly and Company | NKTR-358
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	7,019	11,634	130,087
Amgen, Inc. | Neulasta
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	5,000	5,000	5,000
Baxalta Incorporated / Takeda | Hemophilia, Including ADYNOVATE and ADYNOVITM
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	378	20,328	11,443
Ophthotech Corporation | Fovista
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	0	19,123
Bayer Healthcare LLC | BAY41-6551 (Amikacin Inhale)
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	0	17,931
AstraZeneca AB | MOVANTIK and MOVENTIG
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	0	4,600
Other
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 4,578	$ 535	$ 22,781