License agreements (Details 2) shares in Thousands			1 Months Ended	3 Months Ended			6 Months Ended
	Jun. 30, 2015 USD ($)	Feb. 18, 2015 USD ($) $ / shares	Jan. 31, 2015 USD ($) $ / shares shares	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Jun. 30, 2014 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)
License agreements
Long term investment	$ 67,003,000			$ 67,003,000			$ 67,003,000
Total revenues				162,984,000		$ 99,582,000	322,260,000	$ 189,374,000
Net loss				9,294,000		(36,873,000)	(9,063,000)	(70,830,000)
Unrealized gain on long term investment				27,174,000			27,174,000
Research and development expense				112,445,000		$ 84,683,000	230,809,000	$ 160,269,000
Agenus
License agreements
Fair value of common stock	8.63			8.63			$ 8.63
Acquisition of outstanding voting stock of Agenus (as a percent)							9.00%
Total revenues					$ 4,000,000
Net loss					$ 18,700,000
Unrealized gain on long term investment							$ 27,200,000
Research and development expense				3,800,000			$ 5,600,000
Agenus | Accrued and other liabilities
License agreements
Research and development expense	3,800,000
Agenus | Development Regulatory and Commercialization Milestones
License agreements
Reserved right to elect to co-fund of development costs (as a percent)							30.00%
Agenus | Development Regulatory and Commercialization Milestones | Minimum
License agreements
Range of royalty payments on future global net sales (as a percent)							6.00%
Agenus | Development Regulatory and Commercialization Milestones | Maximum
License agreements
Future contingent milestone payment	155,000,000			155,000,000			$ 155,000,000
Range of royalty payments on future global net sales (as a percent)							12.00%
Agenus | Development Milestones | Maximum
License agreements
Future contingent milestone payment	$ 20,000,000			$ 20,000,000			$ 20,000,000
Agenus | Stock purchase agreement
License agreements
Purchase of common stock under Stock Purchase Agreement (in shares ) | shares			7,760
Purchase price of common stock under Stock Purchase Agreement		$ 39,800,000	$ 35,000,000
Per share price of common stock under Stock Purchase Agreement | $ / shares		5.13	4.51
Minimum period for holding common stock of Agenus		12 months
Total consideration paid		$ 60,000,000
Long term investment		39,800,000
Research and development expense		$ 20,200,000