License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 120,556	$ 41,360	$ 146,422	$ 67,195
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	105,000	25,000	105,001	25,016
Baxter Healthcare [Member] | BAX 855 (Hemophilia) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	9,096	201	10,103	1,499
Roche [Member] | PEGASYS and MIRCERA [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	3,200	2,625	9,614	7,875
Bayer Healthcare LLC [Member] | BAY41-6551 (Amikacin Inhale) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	793	779	3,939	14,604
Amgen, Inc. [Member] | Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250	3,750	3,750
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 1,217	$ 11,505	$ 14,015	$ 14,451