Common Stock (Details) (USD $)	12 Months Ended
	Dec. 31, 2010	Dec. 31, 2012	Mar. 31, 2012	Dec. 31, 2011
Common Stock
Common stock, par value (in dollars per share)	$ 0.01	0.01	0.01	0.01
Common stock
Common stock, authorized shares		200,000,000	200,000,000	138,500,000
Common stock, issued shares		95,825,000		11,834,000
Common stock, outstanding shares		95,825,000		11,834,000
Shares reserved for future issuance
Conversion of Series B, Series C, Series D, Series E, Series F and Series G convertible preferred stock				66,256,000
Convertible preferred stock warrants				302,000
Common stock warrants (in shares)		2,842,000		2,640,000
Option to purchase common stock		18,066,000		17,617,000
Shares reserved for future issuance		20,908,000		86,815,000
Common stock
Common stock
Change in par value	$ (17,547,000)
Common stock, authorized shares		200,000,000	200,000,000	200,000,000
Additional paid-in capital
Common stock
Change in par value	$ 17,547,000