License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 1,097,265	$ 210,965	$ 60,382
Bristol-Myers Squibb [Member] | NKTR-214 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,059,768	0	0
Eli Lilly and Company [Member] | NKTR-358 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	11,634	130,087	0
Baxalta Incorporated/Takeda [Member] | Hemophilia, Including ADYNOVATE and ADYNOVITM [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	20,328	11,443	650
Ophthotech Corporation [Member] | Fovista [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	19,123	1,408
Bayer Healthcare LLC [Member] | BAY41-6551 (Amikacin Inhale) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	17,931	1,429
Amgen, Inc. [Member] | Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	5,000	5,000	5,000
AstraZeneca AB [Member] | MOVANTIK and MOVENTIG [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	4,600	33,000
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 535	$ 22,781	$ 18,895