License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 6,208	$ 17,785	$ 102,948	$ 25,866
AstraZeneca AB [Member] \| MOVANTIKTM (NKTR-118) and MOVANTIKTM fixed-dose combination program (NKTR-119) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	0	0	90,000	0
Roche [Member] \| PEGASYS and MIRCERA [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	3,197	3,219	6,408	6,415
Amgen, Inc. [Member] \| Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250	2,500	2,500
Bayer Healthcare LLC [Member] \| BAY41-6551 (Amikacin Inhale) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	395	2,393	1,205	3,146
Baxalta [Member] \| BAX 855 (Hemophilia) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	88	669	197	1,006
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 1,278	$ 10,254	$ 2,638	$ 12,799