License and Collaboration Agreements - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	0 Months Ended		0 Months Ended						3 Months Ended	0 Months Ended				1 Months Ended	3 Months Ended	12 Months Ended	1 Months Ended	2 Months Ended			1 Months Ended	3 Months Ended	12 Months Ended	1 Months Ended		12 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2013	Sep. 25, 2013 Naloxegol [Member]	Dec. 31, 2013 Naloxegol [Member] US and EU Commercial Launch [Member]	Sep. 16, 2013 AstraZeneca AB [Member]	Sep. 16, 2013 AstraZeneca AB [Member] January 15, 2015 [Member]	Sep. 16, 2013 AstraZeneca AB [Member] Second Installment [Member]	Sep. 16, 2013 AstraZeneca AB [Member] January 15, 2017 [Member]	Sep. 16, 2013 AstraZeneca AB [Member] January 15, 2018 [Member]	Dec. 31, 2013 AstraZeneca AB [Member] FDA Acceptance [Member]	Dec. 31, 2009 AstraZeneca AB [Member] Naloxegol (NKTR-118) and Naloxegol Fixed-dose Combination Program (NKTR-119) [Member] Upfront Payment Arrangement [Member]	Sep. 16, 2013 AstraZeneca AB [Member] Naloxegol [Member]	Dec. 31, 2013 AstraZeneca AB [Member] Naloxegol [Member]	Dec. 31, 2013 AstraZeneca AB [Member] Naloxegol [Member] Pre-approval Cardiovascular Safety Study Not Required [Member]	Dec. 31, 2013 AstraZeneca AB [Member] Naloxegol Fixed-dose Combination Program [Member]	Dec. 31, 2009 Roche [Member] License Extension Option [Member]	Dec. 31, 2013 Roche [Member] MIRCERA [Member]	Dec. 31, 2013 Roche [Member] MIRCERA [Member]	Feb. 29, 2012 Roche [Member] MIRCERA [Member] Performance-based Milestone Payments [Member]	Feb. 29, 2012 Roche [Member] MIRCERA [Member] Upfront Payment Arrangement [Member]	Dec. 31, 2013 Roche [Member] PEGASYS [Member]	Dec. 31, 2013 Roche [Member] PEGASYS and MIRCERA [Member]	Dec. 31, 2007 Bayer Healthcare LLC [Member]	Jun. 30, 2013 Bayer Healthcare LLC [Member]	Dec. 31, 2013 Bayer Healthcare LLC [Member]	Dec. 31, 2007 Bayer Healthcare LLC [Member] Performance-based Milestone Payments [Member]	Dec. 31, 2007 Bayer Healthcare LLC [Member] Upfront Payment Arrangement [Member]	Dec. 31, 2013 Affymax, Inc. [Member] OMONTYS [Member]	Dec. 31, 2010 Amgen, Inc. [Member]	Dec. 31, 2013 Amgen, Inc. [Member]	Dec. 31, 2013 Baxter Healthcare [Member] BAX 855 (Hemophilia) [Member]	Dec. 31, 2013 Baxter Healthcare [Member] BAX 855 (Hemophilia) [Member] Upfront Payment Arrangement [Member]	Dec. 31, 2013 Other Member [Member]
Deferred Revenue Arrangement [Line Items]
Potential future additional payments for development milestones	$ 144.3																							$ 50.0						$ 28.0		$ 66.3
Received upfront and milestone payments										125.0					31.0			22.0	5.0						20.0	40.0		50.0			4.0
Contingent payments receivable based on development events regulatory to be pursued and completed solely by others			140.0						70.0			175.0	35.0	75.0
Development milestones achieved		25.0																					10.0
Contingent repayments of payment received				70.0	10.0	10.0	20.0	30.0
Accrued interest rate				4.50%
Reduction on non-U.S. royalty for repayment											50.00%
Potential reduction in US royalty rate for repayment											2.00%
Maximum potential reduction in royalties											35.0
Deferred revenue																16.1	16.1			10.3	6.9			22.5					34.2
Expected consideration																	27.0
Consideration received for product delivered in 2013																18.6
Performance milestone payments recorded as a liability to Bayer																						10.0
Deferred revenue recognized																											$ 6.7