Accrued Expenses (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Components of accrued expenses
Research and development contract costs	$ 3,530	$ 2,425
Payroll and benefits	2,214	3,267
Professional fees	2,399	592
Short-term portion of accrued settlement payment	966	874
Other	1,552	1,255
Total accrued expenses	$ 10,661	$ 8,413