License and Collaboration Agreements - Additional Information (Detail) (USD $)	12 Months Ended	1 Months Ended			12 Months Ended	1 Months Ended	3 Months Ended	0 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2009	Feb. 29, 2012	Jun. 30, 2013	Dec. 31, 2007	Jun. 30, 2014	Dec. 31, 2009	Sep. 16, 2014	Dec. 31, 2010	Dec. 31, 2013
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones	$ 130,300,000
MOVANTIK [Member] | US and EU Commercial Launch [Member]
Deferred Revenue Arrangement [Line Items]
Contingent payments receivable based on development events regulatory to be pursued and completed solely by others	140,000,000
MOVANTIK [Member] | United States [Member]
Deferred Revenue Arrangement [Line Items]
Contingent payments receivable based on development events regulatory to be pursued and completed solely by others	100,000,000
MOVANTIK [Member] | European Union [Member]
Deferred Revenue Arrangement [Line Items]
Contingent payments receivable based on development events regulatory to be pursued and completed solely by others	40,000,000
Roche [Member] | License Extension Option [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments		31,000,000
Roche [Member] | MIRCERA [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue	10,700,000
Allocated consideration			27,000,000
Consideration received for product delivered in 2013	18,600,000
Roche [Member] | MIRCERA [Member] | Performance-based Milestone Payments [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments			22,000,000
Roche [Member] | MIRCERA [Member] | Upfront Payment Arrangement in 2007 [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments			5,000,000
Roche [Member] | PEGASYS [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue	5,100,000
Roche [Member] | PEGASYS and MIRCERA [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue	4,600,000
Bayer Healthcare LLC [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones	50,000,000
Deferred revenue	20,800,000
Payment made to Bayer for cost of Phase 3 clinical trial				10,000,000
Bayer Healthcare LLC [Member] | Performance-based Milestone Payments [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments	30,000,000
Development milestone achieved in 2013	10,000,000
Bayer Healthcare LLC [Member] | Upfront Payment Arrangement in 2007 [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments					40,000,000
Ophthotech Corporation [Member] | Fovista [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones	9,500,000
Received upfront and milestone payments						19,750,000
Deferred revenue	18,900,000
AstraZeneca AB [Member] | MOVANTIKTM (NKTR-118) and MOVANTIKTM fixed-dose combination program (NKTR-119) [Member] | Upfront Payment Arrangement in 2007 [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments							125,000,000
AstraZeneca AB [Member] | MOVANTIK [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments								70,000,000
Contingent payments receivable based on development events regulatory to be pursued and completed solely by others	140,000,000
Potential reduction in U.S. royalty rate for repayment								2.00%
Percentage of post approval study costs to repay								33.00%
Maximum potential reduction in royalties								35,000,000
AstraZeneca AB [Member] | MOVANTIK [Member] | Pre-approval Cardiovascular Safety Study Not Required [Member]
Deferred Revenue Arrangement [Line Items]
Contingent payments received based on development events								35,000,000
AstraZeneca AB [Member] | Movantik Fixed-dose Combination Program [Member]
Deferred Revenue Arrangement [Line Items]
Contingent payments receivable based on development events regulatory to be pursued and completed solely by others	75,000,000
Baxter Healthcare [Member] | BAX 855 (Hemophilia) [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones	20,000,000
Deferred revenue	0
Development milestones achieved	8,000,000
Amgen, Inc. [Member]
Deferred Revenue Arrangement [Line Items]
Received upfront and milestone payments									50,000,000
Deferred revenue	29,200,000
Affymax, Inc. [Member] | OMONTYS [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue recognized										6,700,000
Other [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones	53,800,000
Development milestones achieved	$ 9,000,000