Fair Value of Financial Instruments - Fair Value of Preferred Stock Warrant Liabilities (Details) (Warrants, USD $) In Thousands, unless otherwise specified	12 Months Ended	1 Months Ended
	Dec. 31, 2011 Preferred stock	Mar. 31, 2011 Series C Preferred Stock	Mar. 31, 2011 Series D Preferred Stock	Mar. 31, 2011 Series E preferred stock
Changes in the fair value of preferred stock warrant liability [Roll Forward]
Fair value at beginning of period	$ 39,756
Changes in fair value of preferred stock warrant liabilities recorded in the statement of operations	42,559
Exercise of preferred stock warrants	(82,315)
Fair value at end of period	0
Weighted-Average Assumptions Used to Determine Fair Value of Preferred Stock Warrants
Risk-free interest rate		0.10%	0.10%	0.10%
Expected term		0 years	0 years	0 years
Estimated dividend yield		0.00%	0.00%	0.00%
Weighted-average estimated volatility		43.10%	43.10%	43.10%
Fair value		$ 3,905	$ 56,445	$ 21,965