Collaboration Agreements (Sanofi) (Details) $ in Thousands	1 Months Ended		3 Months Ended					6 Months Ended	9 Months Ended		12 Months Ended			13 Months Ended
	Jul. 31, 2015 USD ($)	Nov. 30, 2009 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Sep. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Jun. 30, 2014	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jan. 31, 2015 USD ($)
Collaboration Agreement [Line Items]
Number of development milestone payments the Company received								3,000,000
Licenses Revenue			$ 17,529			$ 8,166			$ 56,817	$ 23,496
Period for Achieving Sales Target for Milestone Payment, Rolling Basis					12 months			12 months
Revenue from Related Parties			224,735			132,925			593,201	406,028
Research and development			425,924			$ 337,728			$ 1,159,367	919,608
Number of sales milestone payments the Company received					1	2		5
ZALTRAP Agreement
Collaboration Agreement [Line Items]
Percentage of repayment of development balance out of profits									50.00%
Deferred Revenue, Revenue Recognized					$ 14,900
Licenses Revenue			9,000						$ 32,000
Net profit (loss) from commercialization of products under collaboration agreement			0			$ (1,008)			0	(4,912)
Reimbursement of Regeneron research and development expenses			0			1,261			686	3,691
Contracts Revenue			0			756			15,236	4,417
Revenue from Related Parties			0			1,009			15,922	3,196
Antibody Collaboration
Collaboration Agreement [Line Items]
Net profit (loss) from commercialization of products under collaboration agreement			(74,865)			(12,830)			(143,583)	(17,125)
Recognition of Deferred Revenue			2,561			2,561			7,683	7,683
Annual funding maximum of research activities per amended agreement		$ 160,000
Reduction of Funding for Research Activities Per Agreement	$ 75,000
Reimbursement of Regeneron research and development expenses			205,114			140,497			585,450	405,212
Contracts Revenue			53,341			1,688			89,145	7,062
Revenue from Related Parties			186,151			131,916			$ 538,695	402,832
Percentage of Trial Costs borne by collaborating party									80.00%
Percentage of Trial Costs borne by entity									20.00%
Payments for Purchase of Other Assets						67,500
Research and Development Asset Acquired Other than Through Business Combination, Written-off						33,800
Minimum IO Discovery Agreement Term	3 years
PDGF
Collaboration Agreement [Line Items]
Number of Payments the Company made				1			2
Other Research and Development Expense				$ 10,000			$ 5,000
Milestone payment									$ 20,000
IO Discovery Agreement
Collaboration Agreement [Line Items]
Potential future R&D expenses	$ 1,090,000
Funding Maximum of Research Activities Per Agreement	$ 825,000
Minimum IO Discovery Agreement Term	5 years
Additional years to extend the agreement	3 years
Excess Share of profit not required to to be applied to reimburse development cost	10.00%
Deferred Revenue, Additions	$ 265,000
IO License and Collaboration Agreement
Collaboration Agreement [Line Items]
Excess Share of profit not required to to be applied to reimburse development cost	10.00%
Period of Notice to Opt Out of Further Development and or Commercialization	12 months
Deferred Revenue, Additions	$ 375,000
IO License and Collaboration Agreement | PD-1
Collaboration Agreement [Line Items]
Maximum amount of sales milestone payments if total sales achieve specific levels	375,000
Levels of twelve month sales at which sales milestone payments would be received	$ 2,000,000
Period for Achieving Sales Target for Milestone Payment, Rolling Basis	12 months
Maximum amount of shared development costs	$ 650,000
IO Agreement
Collaboration Agreement [Line Items]
Deferred Revenue, Additions			640,000
Immuno-oncology Agreement
Collaboration Agreement [Line Items]
Recognition of Deferred Revenue			20,000			0			20,000	0
Reimbursement of Regeneron research and development expenses			18,584			0			18,584	0
Revenue from Related Parties			38,584			0			$ 38,584	0
Minimum [Member] | ZALTRAP Agreement
Collaboration Agreement [Line Items]
Percentage of net sales paid by the related party									15.00%
Maximum [Member] | ZALTRAP Agreement
Collaboration Agreement [Line Items]
Percentage of net sales paid by the related party									30.00%
New Funding | IO Discovery Agreement
Collaboration Agreement [Line Items]
Funding Maximum of Research Activities Per Agreement	750,000
Previous Funding under Antibody Discovery Agreement | IO Discovery Agreement
Collaboration Agreement [Line Items]
Funding Maximum of Research Activities Per Agreement	$ 75,000
PDGF
Collaboration Agreement [Line Items]
Number of development milestone payments the Company received				1			2
Percentage of repayment of development balance out of profits									50.00%
Deferred Revenue, Additions							$ 2,500							$ 25,500
Praluent and sarilumab [Member] | Antibody Collaboration
Collaboration Agreement [Line Items]
Research and development			$ 25,100			$ 28,400			$ 72,600	$ 81,300
Scenario, Forecast [Member] | Antibody Collaboration
Collaboration Agreement [Line Items]
Annual funding maximum of research activities per amended agreement											$ 130,000	$ 130,000	$ 145,000