License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 153,289	$ 80,872	$ 30,127
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	105,001	25,016	59
Roche [Member] | PEGASYS and MIRCERA [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	12,845	18,382	7,146
Baxter Healthcare [Member] | BAX 855 (Hemophilia) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	10,258	1,702	6,238
Amgen, Inc. [Member] | Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	5,000	5,035	5,000
Bayer Healthcare LLC [Member] | BAY41-6551 (Amikacin Inhale) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	4,717	15,293	2,971
Affymax, Inc. [Member] | OMONTYS [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue		7,149	2,829
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 15,468	$ 8,295	$ 5,884