Stock-Based Compensation (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Stock-based compensation expense
Total stock-based compensation expense	$ 801	$ 867	$ 2,359	$ 2,506
Research and development
Stock-based compensation expense
Total stock-based compensation expense	612	648	1,797	1,861
General and administrative
Stock-based compensation expense
Total stock-based compensation expense	189	219	562	645
Employee stock options
Stock-based compensation expense
Total stock-based compensation expense	765	774	2,222	2,196
Restricted stock
Stock-based compensation expense
Total stock-based compensation expense	$ 36	$ 93	$ 137	$ 310