License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 46,475	$ 120,556	$ 149,423	$ 146,422
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	40,000	105,000	130,000	105,001
Roche [Member] | PEGASYS and MIRCERA [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	3,212	3,200	9,619	9,614
Amgen, Inc. [Member] | Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250	3,750	3,750
Bayer Healthcare LLC [Member] | BAY41-6551 (Amikacin Inhale) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	357	793	1,562	3,939
Baxalta Incorporated [Member] | BAX 855 (Hemophilia) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	409	9,096	607	10,103
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 1,247	$ 1,217	$ 3,885	$ 14,015