License and Collaboration Agreements (Details) (USD $)	3 Months Ended								12 Months Ended						1 Months Ended	12 Months Ended			1 Months Ended	3 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended		1 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Sanofi Phase 2 clinical trials in breast cancer and non-small cell lung cancer and ovarian cancer	Dec. 31, 2011 Sanofi Phase 2 clinical trials in breast cancer and non-small cell lung cancer and ovarian cancer	Dec. 31, 2010 Sanofi Phase 2 clinical trials in breast cancer and non-small cell lung cancer and ovarian cancer	Nov. 30, 2009 License and Collaboration Agreements Sanofi	Dec. 31, 2012 License and Collaboration Agreements Sanofi	Dec. 31, 2011 License and Collaboration Agreements Sanofi	Dec. 31, 2010 License and Collaboration Agreements Sanofi	Jul. 31, 2009 License and Collaboration Agreements GTC	Dec. 31, 2012 License and Collaboration Agreements GTC	Dec. 31, 2012 License and Collaboration Agreements GTC	Dec. 31, 2011 License and Collaboration Agreements GTC	Dec. 31, 2010 License and Collaboration Agreements GTC	Jul. 31, 2009 License and Collaboration Agreements GTC Series C convertible preferred stock	Dec. 31, 2012 License and Collaboration Agreements PharmaEngine	Dec. 31, 2011 License and Collaboration Agreements PharmaEngine	May 31, 2011 License and Collaboration Agreements PharmaEngine Development and regulatory milestone	May 31, 2011 License and Collaboration Agreements PharmaEngine Sales milestone
License and collaboration agreements
Upfront license fee received															$ 60,000,000
Milestone payments received												5,000,000	10,000,000	10,000,000
Expected development period from the effective date of agreement															12 years				19 years
License agreement termination period																				3 months
Additional revenue recongnized due to a change in estimate																				657,000
Recognized revenue under collaboration agreements
Upfront payment																5,000,000	5,000,000	5,000,000
Milestone payment																2,975,000	2,616,000	949,000
Development services																36,905,000	25,053,000	13,279,000
Manufacturing services and other																3,307,000	1,456,000	630,000
Total																48,187,000	34,125,000	19,858,000
Assets and liabilities related to collaboration agreement
Accounts receivable, billed																1,577,000	4,478,000
Accounts receivable, unbilled																7,690,000	2,925,000
Deferred revenues																79,913,000	84,466,000			553,000	553,000	1,279,000	1,356,000
Collaborative arrangement additional information
Shares received as consideration under the license agreement																								662,000
Fair value of shares received as consideration under the license agreement																								1,469,000
Revenue recognized	14,191,000	11,323,000	12,063,000	11,344,000	12,577,000	8,582,000	6,595,000	6,461,000	48,921,000	34,215,000	20,305,000										733,000	76,000	76,000
Maximum milestone payment obligation																											80,000,000	130,000,000
Research and development expenses									125,858,000	100,630,000	58,278,000														6,200,000	11,200,000
Amounts payable related to the agreement																									$ 345,000	$ 280,000