Collaboration Agreements (Sanofi) (Details) (USD $)	3 Months Ended			6 Months Ended
	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2013 family	Jun. 30, 2014	Jun. 30, 2013 family
Collaboration Agreement [Line Items]
Research and development	$ 294,501,000		$ 187,463,000	$ 581,880,000	$ 367,762,000
Revenue from Related Parties	142,595,000		85,529,000	273,103,000	184,802,000
ZALTRAP Agreement
Collaboration Agreement [Line Items]
Net profit (loss) from commercialization of products under collaboration agreement	(692,000)		(8,216,000)	(3,904,000)	(16,005,000)
Reimbursement of Regeneron research and development expenses	1,338,000		1,992,000	2,430,000	4,081,000
Contracts Revenue	1,484,000		2,227,000	3,661,000	4,084,000
Revenue from Related Parties	2,130,000		(3,997,000)	2,187,000	(7,840,000)
Ang2
Collaboration Agreement [Line Items]
Research and Development in Process			10,000,000		10,000,000
Antibody Collaboration
Collaboration Agreement [Line Items]
Net profit (loss) from commercialization of products under collaboration agreement	(4,295,000)		0	(4,295,000)	0
Number of Payments the Company made		2	2		2
Research and Development in Process	0		20,000,000	0	20,000,000
Number of families of novel antibodies			2		2
Percentage of Trial Costs borne by collaborating party				80.00%
Percentage of Trial Costs borne by entity				20.00%
Research and development	29,100,000			52,900,000
Other Research and Development Expense		5,000,000		5,000,000
Milestone payment				30,000,000
Reimbursement of Regeneron research and development expenses	137,893,000		105,274,000	264,715,000	204,898,000
Contracts Revenue	6,867,000		4,252,000	10,496,000	7,744,000
Revenue from Related Parties	140,465,000		89,526,000	270,916,000	192,642,000
PDGF
Collaboration Agreement [Line Items]
Research and Development in Process			$ 10,000,000		$ 10,000,000