License and Collaboration Agreements - License, Collaboration and Other Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 8,373	$ 46,475	$ 50,829	$ 149,423
AstraZeneca AB [Member] | MOVANTIKTM and MOVANTIKTM fixed-dose combination program [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	3,000	40,000	31,000	130,000
Roche [Member] | PEGASYS and MIRCERA [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,929	3,212	5,771	9,619
Amgen, Inc. [Member] | Neulasta [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	1,250	1,250	3,750	3,750
Daiichi Sankyo Europe GmbH [Member] | ONZEALDTM (NKTR-102) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	216	0	3,474	0
Bayer Healthcare LLC [Member] | BAY41-6551 (Amikacin Inhale) [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	357	357	1,072	1,562
Baxalta Incorporated [Member] | ADYNOVATETM [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	336	409	648	607
Other [Member]
License And Collaboration Agreements [Line Items]
License, collaboration and other revenue	$ 1,285	$ 1,247	$ 5,114	$ 3,885