Stock-Based Compensation (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Costs and expenses:
Total stock-based compensation expense	$ 1,224	$ 1,966	$ 2,607	$ 3,929
Research and development [Member]
Costs and expenses:
Total stock-based compensation expense	646	900	1,421	1,811
General and administrative [Member]
Costs and expenses:
Total stock-based compensation expense	$ 578	$ 1,066	$ 1,186	$ 2,118