Common Stock (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Common Stock
Common stock, shares authorized	200,000	200,000	138,500
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01
Common stock, shares issued	94,029		11,834
Common stock, shares outstanding	94,029		11,834
Shares reserved for future issuance
Conversion of Series B, Series C, Series D, Series E, Series F and Series G convertible preferred stock			66,256
Convertible preferred stock warrants			302
Common stock warrants	2,891		2,640
Options to purchase common stock	19,812		17,617
Shares reserved for future issuance	22,703		86,815