License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 210,965	$ 60,382	$ 165,604
Eli Lilly and Company [Member] \| NKTR-358 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	130,087
Ophthotech Corporation [Member] \| Fovista [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	19,123	1,408	1,398
Bayer Healthcare LLC [Member] \| BAY41-6551 (Amikacin Inhale) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	17,931	1,429	1,919
Baxalta Incorporated/Shire [Member] \| ADYNOVATE [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	11,443	650	10,694
MAP Pharmaceuticals, Inc. / Allergan [Member] \| SEMPRANA [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	11,000
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 MOVANTIK fixed-dose combination program [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	4,600	33,000	130,000
Daiichi Sankyo Europe GmbH [Member] \| ONZEALDTM (NKTR-102) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	3,811	3,690
Roche [Member] \| PEGASYS and MIRCERA [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue		7,685	12,816
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 7,970	$ 7,520	$ 3,777