License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 131,112	$ 8,373	$ 142,028	$ 50,829
Eli Lilly and Company [Member] | NKTR-358 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	127,553	0	127,553	0
AstraZeneca AB [Member] | MOVANTIK and MOVANTIK fixed-dose combination program [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	3,000	4,600	31,000
Amgen, Inc. [Member] | Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250	3,750	3,750
Bayer Healthcare LLC [Member] | BAY41-6551 (Amikacin Inhale) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	357	357	1,072	1,072
Daiichi Sankyo Europe GmbH [Member] | ONZEALDTM (NKTR-102) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	216	216	647	3,474
Roche [Member] | MIRCERA [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	1,929	0	5,771
Baxalta Incorporated [Member] | ADYNOVATE [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	312	336	357	648
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 1,424	$ 1,285	$ 4,049	$ 5,114