Commitments and Contingencies (Details) (USD $)	1 Months Ended		12 Months Ended			1 Months Ended		3 Months Ended
	Aug. 31, 2012 item	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Nov. 30, 2009 License and Collaboration Agreements Sanofi	Dec. 31, 2012 License and Collaboration Agreements Sanofi	Mar. 31, 2012 Quality control issues related to fill-finish manufacturing services License and Collaboration Agreements Sanofi	Dec. 31, 2012 Quality control issues related to fill-finish manufacturing services License and Collaboration Agreements Sanofi
Operating Leases
Total rent expense			$ 4,317,000	$ 3,235,000	$ 2,846,000
Lease term of additional space		7 years
Aggregate rent due over amended term of lease	31,500,000	2,700,000
Maximum reimbursement for tenant improvements agreed by landlord	6,600,000	500,000
Additional space that the entity will occupy under the amended lease agreement	23,000
Aggregate space that the entity will occupy under the amended lease agreement	109,000
Reimbursement for tenant improvements agreed by landlord in 2012	4,600,000
Reimbursement for tenant improvements agreed by landlord in 2013	1,000,000
Reimbursement for tenant improvements agreed by landlord in 2014	1,000,000
Reimbursement for tenant improvements agreed by landlord recorded in prepaid expenses and other current assets with offsetting entry to deferred rent	5,600,000
Reimbursement for tenant improvements agreed by landlord recorded in other assets with offsetting entry to deferred rent	1,000,000
Tenant improvement reimbursements received			600,000
Additional period of renewal of amended lease with respect to entire leased space, option one	1 year
Additional period of renewal of amended lease with respect to entire leased space, option two	5 years
Future minimum lease payments under noncancelable operating leases
2013			4,319,000
2014			4,439,000
2015			4,601,000
2016			4,735,000
2017			4,838,000
2018 and thereafter			7,427,000
Contractual Matter
Previously billed amount the Company will reimburse									1,200,000
Expected development period from the effective date of agreement						12 years
Reduction in earnings due to reimbursement of previously billed amounts								200,000
Amount accrued by company							$ 851,000