Stock-Based Compensation (Details 2) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Stock-based compensation expense
Stock-based compensation expense	$ 3,322	$ 3,354	$ 4,048
Research and development
Stock-based compensation expense
Stock-based compensation expense	2,485	2,494	3,074
General and administrative
Stock-based compensation expense
Stock-based compensation expense	837	860	974
Employee stock options
Stock-based compensation expense
Stock-based compensation expense	3,082	2,951	3,614
Restricted stock
Stock-based compensation expense
Stock-based compensation expense	$ 240	$ 403	$ 434