License Agreements (Details) (USD $)	12 Months Ended			3 Months Ended	12 Months Ended	1 Months Ended			12 Months Ended			1 Months Ended				12 Months Ended			1 Months Ended		12 Months Ended				1 Months Ended		12 Months Ended	1 Months Ended		12 Months Ended		1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 JAKAFI (ruxolitinib)	Dec. 31, 2012 JAKAFI (ruxolitinib)	Jan. 31, 2010 Collaboration and License Agreement with Novartis	Dec. 31, 2009 Collaboration and License Agreement with Novartis	Nov. 30, 2009 Collaboration and License Agreement with Novartis deliverable	Dec. 31, 2012 Collaboration and License Agreement with Novartis	Dec. 31, 2011 Collaboration and License Agreement with Novartis	Dec. 31, 2010 Collaboration and License Agreement with Novartis	Nov. 30, 2009 Collaboration and License Agreement with Novartis Pre-specified events	Nov. 30, 2009 Collaboration and License Agreement with Novartis Development milestones	Nov. 30, 2009 Collaboration and License Agreement with Novartis Regulatory milestones	Nov. 30, 2009 Collaboration and License Agreement with Novartis Commercialized milestones	Dec. 31, 2011 Collaboration and License Agreement with Novartis LY3009104(INCB28060)	Dec. 31, 2012 Collaboration and License Agreement with Novartis JAKAFI (ruxolitinib)	Dec. 31, 2011 Collaboration and License Agreement with Novartis JAKAFI (ruxolitinib)	Jul. 31, 2010 License, Development and Commercialization Agreement with Lilly	Dec. 31, 2009 License, Development and Commercialization Agreement with Lilly deliverable	Dec. 31, 2012 License, Development and Commercialization Agreement with Lilly	Dec. 31, 2011 License, Development and Commercialization Agreement with Lilly	Dec. 31, 2010 License, Development and Commercialization Agreement with Lilly	Dec. 31, 2010 License, Development and Commercialization Agreement with Lilly Maximum	Dec. 31, 2009 License, Development and Commercialization Agreement with Lilly Pre-specified events Maximum	Dec. 31, 2009 License, Development and Commercialization Agreement with Lilly Development milestones Maximum	Dec. 31, 2012 License, Development and Commercialization Agreement with Lilly Development milestones Phase III	Dec. 31, 2009 License, Development and Commercialization Agreement with Lilly Regulatory milestones Maximum	Dec. 31, 2009 License, Development and Commercialization Agreement with Lilly Commercialized milestones Maximum	Dec. 31, 2010 License, Development and Commercialization Agreement with Lilly LY3009104(INCB28060) Development milestones Phase IIa	Dec. 31, 2010 License, Development and Commercialization Agreement with Lilly LY3009104(INCB28060) Development milestones Phase IIb	Jan. 31, 2006 Collaborative Research and License Agreement with Pfizer day	Dec. 31, 2010 Collaborative Research and License Agreement with Pfizer Phase I
License agreements
Upfront and immediate milestone payment to be received under license agreement								$ 210,000,000			$ 50,000,000	$ 1,100,000,000	$ 162,000,000	$ 450,000,000	$ 500,000,000										$ 665,000,000	$ 150,000,000	$ 50,000,000	$ 365,000,000	$ 150,000,000	$ 30,000,000	$ 19,000,000
Amount recognized and received for the achievement of a predefined milestone																15,000,000		10,000,000
Additional milestone payment received under license agreement									40,000,000	25,000,000	50,000,000						40,000,000				50,000,000		49,000,000
Number of deliverables under license agreement								2												2
Upfront payment received under license agreement							150,000,000													90,000,000												40,000,000
Immediate milestone payment received under license agreement						60,000,000
Reimbursable costs recorded as deferred revenue							10,900,000
Reimbursable costs included in accounts receivable									2,100,000	2,300,000											0.0	0.0
Research and development expenses reimbursed									4,400,000	3,600,000	7,100,000										100,000	200,000	2,800,000
Contract revenues	156,948,000	91,948,000	168,948,000						94,100,000	79,100,000	104,100,000										62,900,000	12,900,000	61,900,000										3,000,000
Range of royalty payments on future global net sales, upper range (as a percent)																								20.00%
Associated future global development costs from the initiation of a Phase IIb trial, if elected to co-develop, percentage																			30.00%	30.00%
Product royalty revenues	$ 3,652,000			$ 3,700,000	$ 3,700,000
Period of notice for termination of license agreement (in days)																																90