License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 3,121	$ 4,875	$ 9,860	$ 1,082,848
Bristol-Myers Squibb Company | NKTR-214
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	0	0	1,059,768
Eli Lilly and Company | NKTR-358
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,500	3,221	5,200	8,627
Amgen, Inc. | Neulasta
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250	3,750	3,750
Baxalta Inc. / Takeda Pharmaceutical Company Ltd. and other
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 371	$ 404	$ 910	$ 10,703