Common Stock (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Common Stock
Common stock, authorized shares	200,000	200,000
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, issued shares	96,360	95,825
Common stock, outstanding shares	96,360	95,825
Shares reserved for future issuance
Common stock warrants (in shares)	2,777	2,842
Options to purchase common stock	20,447	18,066
Shares reserved for future issuance	23,224	20,908