Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2013

Stock-Based Compensation

Summary of Founders' stock activity and related information

	Shares
Unvested at December 31, 2011		2,319,646
Granted		—
Vested		(674,505	)
Unvested at December 31, 2012		1,645,141
Granted		—
Vested		(658,060	)
Unvested at December 31, 2013		987,081

Summary of the Company's stock option activity and related information

A summary of the Company's stock option activity and related information is as follows (in thousands, except share and per share data):

	Shares			Weighted average exercise price per share		Weighted average remaining contractual term (years)		Aggregate intrinsic value
Outstanding at December 31, 2012		1,218,153			3.83		9.34		5,535
Granted		1,537,172			12.87
Exercised		(42,799	)		0.99
Forfeited		(278,158	)		7.07
Cancelled		(21,131	)		4.01
Outstanding at December 31, 2013		2,413,237			9.26		9.05		6,087
Exercisable at December 31, 2013		468,710			3.46		8.28		3,112
Vested and expected to vest at December 31, 2013		1,445,760			8.14		8.90		4,192

Schedule of assumptions used to estimate fair value of each stock-based option award on the grant date using the Black-Scholes option pricing model

	December 31,
	2013	2012	2011
Risk-free interest rate	0.91% - 2.11%	0.8% - 1.78%	1.2% - 1.84%
Dividend yield	—	—	—
Volatility	83% - 91%	79% - 89%	79% - 82%
Expected term (years)	5.1 - 9.93	5.1 - 9.93	6.0 - 9.75