Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2015

	Number of Shares		Weighted-Average Exercise Price Per Share		Weighted-Average Remaining Contractual Term (In years)	Aggregate Intrinsic Value (In thousands)
Outstanding at December 31, 2014	2,911,146		$	5.30	7.87	$	40,586
Granted	972,133		16.96
Exercised	(264,393	)	2.89			3,588
Cancelled	(147,950	)	6.52

Outstanding at September 30, 2015	3,470,936		8.69		7.64	11,396

Exercisable at September 30, 2015	1,649,062		4.36		6.16	8,850

Vested or expected to vest at September 30, 2015	3,238,718		8.34		7.53	11,181

Schedule of estimated assumptions used to calculate weighted-average fair value of options granted

	Nine Months Ended September 30,
	2015		2014
Weighted-average risk-free interest rate	1.70	%	1.93	%
Expected dividend yield	0.00	%	0.00	%
Expected volatility	55	%	61	%
Expected terms	5.9 years		6.0 years

Summary of stock-based compensation expense for stock options granted that was recorded in the Company's results of operations

The following table summarizes the stock-based compensation expense resulting from awards granted under stock incentive plans, including the 2014 ESPP, that was recorded in the Company’s results of operations for the periods presented (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2015		2014		2015		2014
Research and development	$	440	$	127	$	1,017	$	250
Selling, general and administrative	882		425		1,882		807

Total stock-based compensation expense	$	1,322	$	552	$	2,899	$	1,057