Stock Compensation (Tables)

12 Months Ended

Dec. 31, 2014

Stock Compensation

Summary of activity relating to the Company's options to purchase common stock

	Number of Options			Weighted-Average Price Per Share		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
								(in thousands)
Outstanding at December 31, 2013		1,401,101		$	9.59		8.95	$	7,755
Granted		561,500		$	15.03
Forfeited or expired (vested and unvested)		(125,052	)	$	12.97
Exercised		(107,963	)	$	4.38
Outstanding at December 31, 2014		1,729,586		$	11.44		8.43	$	50,155

Summary of information about the stock option plan

	Number of Options		Weighted-Average Price Per Share		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
							(in thousands)
Vested and expected to vest at December 31, 2014		1,671,313	$	11.37		8.41	$	48,588
Exercisable at December 31, 2014		752,397	$	6.61		7.58	$	25,452

Schedule of weighted-average assumptions used to compute the stock-based compensation costs for the stock options granted to employees and non-employees

	Year ended December 31,
	2014			2013			2012
Risk-free interest rate		1.81	%		1.45	%		0.85	%
Dividend yield		—			—			—
Weighted-average expected life of options (years)		6.32			6.26			6.25
Volatility		75	%		74	%		80	%