License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 4,204	$ 13,727
Baxalta Incorporated/Takeda [Member] | ADYNOVATE [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	20	10,011
Eli Lilly and Company [Member] | NKTR-358 [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	2,500	2,354
Amgen, Inc. [Member] | Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 434	$ 112