Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2014

Stock-Based Compensation

Summary of Founders' stock activity and related information

	Shares
Unvested at December 31, 2012		1,645,141
Granted		—
Vested		(658,060	)
Unvested at December 31, 2013		987,081
Granted		—
Vested		(658,060	)
Unvested at December 31, 2014		329,021

Summary of 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, 2013		2,413,237		$	9.26		9.05	$	6,087
Granted		2,464,138			19.12
Exercised		(370,808	)		3.81
Forfeited		(852,564	)		11.51
Cancelled		(25,375	)		5.48
Outstanding at December 31, 2014		3,628,628			16.01		9.11		102,355
Exercisable at December 31, 2014		688,562			8.43		8.07		24,641
Vested and expected to vest at December 31, 2014		2,394,044			15.11		9.01		69,692

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,
	2014	2013	2012
Risk-free interest rate	1.62% - 2.17%	0.91% - 2.11%	0.8% - 1.78%
Dividend yield	—	—	—
Volatility	76% - 84%	83% - 91%	79% - 89%
Expected term (years)	5.3 - 9.97	5.1 - 9.93	5.1 - 9.93