Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended		3 Months Ended		9 Months Ended		1 Months Ended	3 Months Ended
	Aug. 31, 2012 item	Mar. 31, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Nov. 30, 2009 License and Collaboration Agreements Sanofi	Mar. 31, 2012 Quality control issues related to fill-finish manufacturing services License and Collaboration Agreements Sanofi	Sep. 30, 2012 Quality control issues related to fill-finish manufacturing services License and Collaboration Agreements Sanofi
Operating leases
Total rent expense			$ 1.1	$ 0.8	$ 3.1	$ 2.3
Lease term of additional space	7 years	7 years
Aggregate rent due over amended term of lease	31.5	2.7
Maximum reimbursement for tenant improvements agreed by landlord	6.6	0.5
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			4.6		4.6
Reimbursement for tenant improvements agreed by landlord in 2013			1.0		1.0
Reimbursement for tenant improvements agreed by landlord in 2014			1.0		1.0
Reimbursement for tenant improvements agreed by landlord recorded in prepaid expenses and other current assets with offsetting entry to deferred lease benefits			5.6		5.6
Reimbursement for tenant improvements agreed by landlord recorded in other assets with offsetting entry to deferred lease benefits			1.0		1.0
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
Contractual matter
Previously billed amount the Company will reimburse									1.2
Expected development period from the effective date of agreement							12 years
Reduction in earnings due to reimbursement of previously billed amounts								$ 0.2