License and Collaboration Agreements - Additional Information (Detail) (USD $)	12 Months Ended			2 Months Ended	12 Months Ended	3 Months Ended		12 Months Ended	1 Months Ended			12 Months Ended					12 Months Ended	2 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended											3 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009 Roche [Member] License extension option [Member]	Dec. 31, 2012 Roche [Member] Performance-based milestone payments [Member]	Dec. 31, 2010 Amgen, Inc. [Member]	Dec. 31, 2012 Amgen, Inc. [Member]	Dec. 31, 2012 Bayer Healthcare LLC [Member]	Dec. 31, 2007 Bayer Healthcare LLC [Member] Upfront payment arrangement [Member]	Dec. 31, 2007 Bayer Healthcare LLC [Member] Performance-based milestone payments [Member]	Dec. 31, 2012 AstraZeneca AB [Member]	Dec. 31, 2012 Other [Member]	Dec. 31, 2011 Other [Member]	Dec. 31, 2010 Other [Member]	Dec. 31, 2011 Other [Member] Upfront payment arrangement [Member]	Dec. 31, 2012 PEGASYS [Member] Roche [Member]	Dec. 31, 2012 MIRCERA [Member] Roche [Member]	Feb. 29, 2012 MIRCERA [Member] Roche [Member] Upfront payment arrangement [Member]	Dec. 31, 2012 MIRCERA [Member] Roche [Member] Upfront payment arrangement [Member]	Feb. 29, 2012 MIRCERA [Member] Roche [Member] Performance-based milestone payments [Member]	Dec. 31, 2012 OMONTYS [Member] Affymax, Inc. [Member]	Dec. 31, 2011 OMONTYS [Member] Affymax, Inc. [Member]	Dec. 31, 2010 OMONTYS [Member] Affymax, Inc. [Member]	Dec. 31, 2012 Hemophilia [Member] Baxter Healthcare [Member]	Dec. 31, 2011 Hemophilia [Member] Baxter Healthcare [Member]	Dec. 31, 2010 Hemophilia [Member] Baxter Healthcare [Member]	Dec. 31, 2012 Hemophilia B [Member]	Dec. 31, 2012 Hemophilia B [Member] Baxter Healthcare [Member]	Dec. 31, 2012 Naloxegol (NKTR-118) and naloxegol fixed-dose combination program (NKTR-119) [Member] AstraZeneca AB [Member]	Dec. 31, 2011 Naloxegol (NKTR-118) and naloxegol fixed-dose combination program (NKTR-119) [Member] AstraZeneca AB [Member]	Dec. 31, 2010 Naloxegol (NKTR-118) and naloxegol fixed-dose combination program (NKTR-119) [Member] AstraZeneca AB [Member]	Dec. 31, 2009 Naloxegol (NKTR-118) and naloxegol fixed-dose combination program (NKTR-119) [Member] AstraZeneca AB [Member] Upfront payment arrangement [Member]	Dec. 31, 2012 Naloxegol [Member]	Dec. 31, 2012 Naloxegol [Member] AstraZeneca AB [Member]	Dec. 31, 2012 Naloxegol fixed-dose combination program [Member] AstraZeneca AB [Member]
Deferred Revenue Arrangement [Line Items]
Potential future payments for development milestones	$ 161,100,000							$ 60,000,000				$ 73,100,000												$ 28,000,000
Received upfront and milestone payments				31,000,000		50,000,000			40,000,000	20,000,000								5,000,000	16,000,000					4,000,000				5,000,000				125,000,000
Deferred revenue							39,200,000	24,500,000								15,400,000	13,000,000				7,100,000			1,300,000
Expected consideration					11,000,000												27,000,000			22,000,000
Revenue recognized as contractual obligations are completed															5,000,000		3,000,000										3,900,000
Performance milestone to be used to reimburse Bayer for future clinical trial costs								10,000,000
Substantive milestone revenue																					2,000,000
Contingent payments receivable based on development events regulatory to be pursued and completed solely by others											95,000,000																						140,000,000	235,000,000	75,000,000
License, collaboration and other revenue	$ 30,127,000	$ 36,289,000	$ 124,372,000									$ 5,884,000	$ 11,186,000	$ 3,686,000							$ 2,829,000	$ 3,838,000	$ 1,867,000	$ 6,238,000	$ 5,646,000	$ 1,701,000			$ 59,000	$ 2,496,000	$ 107,854,000