Summary of Significant Accounting Policies (Details 7) (USD $)	12 Months Ended				1 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Apr. 30, 2012	Apr. 30, 2012 Initial public offering Common stock
Public Offering
Convertible preferred stock converted into common stock (in shares)					66,255,529
Convertible Preferred Stock and Convertible Preferred Stock Warrants
Number of preferred stock authorized (in shares)	10,000,000	10,000,000		10,000,000
Par value of preferred stock ( in dollars per share )	$ 0.01	$ 0.01		$ 0.01
Change in fair value of convertible preferred stock warrants	$ 587,000	$ (864,000)	$ (74,000)