License agreements - Agenus (Details) $ / shares in Units, shares in Thousands, $ in Thousands		1 Months Ended		3 Months Ended		9 Months Ended
	Feb. 18, 2015 USD ($) $ / shares	Nov. 30, 2015 item	Jan. 31, 2015 USD ($) item $ / shares shares	Sep. 30, 2016 USD ($) $ / shares	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) $ / shares	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	[1]
License agreements
Long term investment				$ 55,745		$ 55,745		$ 35,248
Total revenues				269,469	$ 187,611	779,221	$ 509,870
Unrealized gain (loss) on long term investment				24,301	(31,289)	20,497	(4,115)
Research and development expense				$ 143,184	132,073	$ 420,276	362,882
Agenus
License agreements
Number of program targets | item		3	4
Period of notice for termination of license agreement			12 months
Fair value of common stock | $ / shares				$ 7.18		$ 7.18
Acquisition of outstanding voting stock of Agenus (as a percent)						9.00%
Total revenues				$ 6,600		$ 12,600
Net loss				(28,300)		(60,100)
Unrealized gain (loss) on long term investment				24,300		20,500
Research and development expense				3,900	$ 3,800	12,000	$ 9,400
Agenus | Accrued and other liabilities
License agreements
Accrued and other liabilities				10,300		$ 10,300
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		$ 155,000
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		$ 20,000
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		$ 35,000
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
Long term investment	39,800
Research and development expense	$ 20,200
Agenus | Stock purchase agreement | Maximum
License agreements
Percentage of outstanding voting stock that may be acquired			15.00%

[1] The condensed consolidated balance sheet at December 31, 2015 has been derived from the audited financial statements at that date.