Stockholders' Equity (Tables) - 10Q

3 Months Ended

Mar. 31, 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	516,954		18.20
Exercised	(157,324	)	2.38			2,067
Cancelled	(46,724	)	7.97
Outstanding at March 31, 2015	3,224,052		7.47		8.03	25,954
Exercisable at March 31, 2015	1,543,881		2.74		6.56	19,733
Vested or expected to vest at March 31, 2015	2,827,095		7.09		7.89	23,822

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

	Three Months Ended March 31,
	2015		2014
Weighted-average risk-free interest rate	1.70	%	2.04	%
Expected dividend yield	0.00	%	0.00	%
Expected volatility	56	%	62	%
Expected terms	6.1 years		6.1 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 for stock options granted to employees and nonemployees, as well as stock-based compensation expense for the 2014 ESPP that was recorded in the Company’s results of operations for the three months ended March 31, 2015 and 2014 (in thousands):

	Three Months Ended March 31,
	2015		2014
Research and development	$	280	$	56
Selling, general and administrative	442		183
Total stock-based compensation expense	$	722	$	239