Stock-Based Compensation (Details 2) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Stock-based compensation expense
Total stock-based compensation expense	$ 731	$ 812	$ 1,558	$ 1,639
Research and development
Stock-based compensation expense
Total stock-based compensation expense	562	600	1,185	1,213
General and administrative
Stock-based compensation expense
Total stock-based compensation expense	169	212	373	426
Employee stock options
Stock-based compensation expense
Total stock-based compensation expense	702	714	1,457	1,422
Restricted stock
Stock-based compensation expense
Total stock-based compensation expense	$ 29	$ 98	$ 101	$ 217