Collaboration Agreements (Sanofi) (Details) - USD ($) $ in Thousands		1 Months Ended		3 Months Ended		12 Months Ended
	Mar. 31, 2016	Jul. 31, 2015	Nov. 30, 2007	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jan. 07, 2018
Collaboration Agreements [Line Items]
Accounts receivable - trade, net						$ 1,538,642	$ 1,343,368
Deferred revenue from Sanofi, current portion						177,746	115,267
Research and Development Expense						$ 2,075,142	2,052,295	$ 1,620,577
Maximum shares the collaborator could sell						1,400,000
Revenue from Related Parties						$ 877,193	658,665	758,873
Other Revenue, Net						338,519	119,102	74,889
Payments to Acquire Marketable Securities						$ 1,277,140	809,419	557,105
PDGFR-beta outside the US
Collaboration Agreements [Line Items]
Percentage of development cost for the territory outside the United States to be paid for under the collaboration	50.00%
Deferred Revenue, Additions					$ 25,500
Percentage of global development cost to be paid by the collaboration partner under the collaboration	25.00%
Collaboration Agreement with Sanofi
Collaboration Agreements [Line Items]
Common Stock, shares issued (in shares)						23,880,537
IO Agreement [Member]
Collaboration Agreements [Line Items]
Deferred Revenue, Additions							640,000
Antibody Collaboration
Collaboration Agreements [Line Items]
Accounts receivable - trade, net						$ 121,001	47,268
Deferred revenue from Sanofi, current portion						117,682	98,741
Contingent reimbursement obligation						2,558,000
Recognition of Deferred Revenue						119,076	28,379	12,322
Net profit (loss) from commercialization of products under collaboration agreement						(442,610)	(459,058)	(240,042)
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned						508,364	564,900	735,439
Contracts Revenue						368,859	305,947	155,271
Research and Development Expense						91,800	108,600	92,600
Revenue from Related Parties						$ 553,689	440,168	662,990
Proceeds from Collaborators			$ 85,000
Percentage of repayment of development balance out of profits						50.00%
Annual funding maximum of research activities per amended agreement						$ 130,000	130,000	145,000
Percentage of Trial Costs borne by collaborating party						80.00%
Percentage of Trial Costs borne by entity						20.00%
Percentage of trial costs to be reimbursed due to profitability of agreement						30.00%
Excess Share of profit not required to to be applied to reimburse development cost						10.00%
Starting share of profits outside the United States, based on sales, for collaborating party						65.00%
Starting share of profits outside the United States, based on sales, for Company						35.00%
Ending share of profits outside the United States, based on sales, for collaborating party						55.00%
Ending share of profits outside the United States, based on sales, for Company						45.00%
Share of losses outside the United States, for collaborating party						55.00%
Share of losses outside the United States, for Company						45.00%
Maximum amount of sales milestone payments if total sales achieve specific levels						$ 250,000
Starting specified levels of annual sales at which sales milestone payments may be received						$ 1,000,000
Period for Achieving Sales Target for Milestone Payment, Rolling Basis						12 months
Period of Notice to Opt Out of Further Development and or Commercialization						12 months
Immuno-oncology Agreement [Member]
Collaboration Agreements [Line Items]
Accounts receivable - trade, net						$ 59,274	40,647
Deferred revenue from Sanofi, current portion						440,000	520,000
Contingent reimbursement obligation						22,000
Recognition of Deferred Revenue						83,523	80,000	40,000
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned						239,981	138,497	39,961
Revenue from Related Parties						323,504	218,497	79,961
ZALTRAP Agreement
Collaboration Agreements [Line Items]
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned						0	0	686
Contracts Revenue						0	0	15,236
Deferred Revenue, Revenue Recognized				$ 14,900
Revenue from Related Parties						0	0	15,922
Related Party Transaction, Other Revenues from Transactions with Related Party						$ 24,800	$ 26,200	$ 38,800
IO Discovery Agreement [Member]
Collaboration Agreements [Line Items]
License agreement term		5 years
Deferred Revenue, Additions		$ 265,000
Potential future R&D expenses		1,090,000
Funding Maximum of Research Activities Per Agreement		$ 825,000
Additional years to extend the agreement		3 years
Excess Share of profit not required to to be applied to reimburse development cost		10.00%
IO License and Collaboration Agreement [Member]
Collaboration Agreements [Line Items]
Deferred Revenue, Additions		$ 375,000
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
PD-1 [Member] | IO License and Collaboration Agreement [Member]
Collaboration Agreements [Line Items]
Levels of twelve month sales at which sales milestone payments would be received		$ 2,000,000
Maximum amount of sales milestone payments if total sales achieve specific levels		$ 375,000
Period for Achieving Sales Target for Milestone Payment, Rolling Basis		12 months
Minimum | ZALTRAP Agreement
Collaboration Agreements [Line Items]
Percentage of aggregate net sales to be paid by the related party in such calendar year						15.00%
Maximum | ZALTRAP Agreement
Collaboration Agreements [Line Items]
Percentage of aggregate net sales to be paid by the related party in such calendar year						30.00%
Subsequent Event [Member] | IO License and Collaboration Agreement [Member]
Collaboration Agreements [Line Items]
Maximum amount of shared development costs									$ 1,640,000
Increase amount of shared development costs									$ 990,000