Collaboration Revenue (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Research Collaboration and Licensing Arrangements [Line Items]
Sanofi collaboration revenue	$ 99,273	$ 85,005
Bayer HealthCare collaboration revenue	14,907	12,483
Antibody
Research Collaboration and Licensing Arrangements [Line Items]
Sanofi collaboration revenue	103,115	83,407
Collaboration Agreement with Sanofi | ZALTRAP
Research Collaboration and Licensing Arrangements [Line Items]
Net profit (loss) from commercialization of products under collaboration agreement	(7,789)	(3,705)
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned	2,563	2,820
Recognition of Deferred Revenue	1,384	2,483
Sanofi collaboration revenue	(3,842)	1,598
Collaboration Agreement with Sanofi | Antibody
Research Collaboration and Licensing Arrangements [Line Items]
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned	100,554	80,855
Recognition of Deferred Revenue	2,162	2,153
Collaboration Agreement with Sanofi | VelociGene
Research Collaboration and Licensing Arrangements [Line Items]
Recognition of Deferred Revenue	399	399
Collaboration Agreement with Bayer HealthCare LLC [Member]
Research Collaboration and Licensing Arrangements [Line Items]
Recognition of Deferred Revenue	1,977	1,977
Collaboration Agreement with Bayer HealthCare LLC [Member] | EYLEA
Research Collaboration and Licensing Arrangements [Line Items]
Net profit from commercialization of products under collaboration agreement	6,362
Research and Development Arrangement, Contract to Perform for Others, Compensation Earned	5,971	10,506
Reimbursement of commercial expenses	$ 597