Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2014

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Assumptions used to Determine Fair Value of Stock Options Granted

 The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors are as follows, presented on a weighted average basis (the Company did not grant any stock options to employees or directors during the year ended December 31, 2012):

	Year Ended     December 31,
	2014			2013
Risk-free interest rate		1.90	%		1.12	%
Expected term (in years)		6.25			6.25
Expected volatility		90	%		85	%
Expected dividend yield		0	%		0	%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity since December 31, 2013:

	Shares Issuable Under Options			Weighted Average Exercise Price		Average Remaining Contractual Term		Aggregate Intrinsic Value
	(In years)
Outstanding as of December 31, 2013		1,310,330		$	1.88		7.8	$	10,185
Granted		698,642			15.56
Exercised		(398	)		6.78
Forfeited		—
Outstanding as of December 31, 2014		2,008,574		$	6.65		7.7	$	222,584
Options vested and expected to vest as of December 31, 2014		2,008,574		$	6.65		7.7	$	222,584
Options exercisable as of December 31, 2014		916,818		$	1.64		6.3	$	26,767

Summary of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock

The Company recorded stock-based compensation expense related to stock options and restricted common stock in the following expense categories within its statements of operations:

	Year Ended December 31,
	2014		2013		2012
Research and development	$	490	$	176	$	68
General and administrative		1,063		219		53
	$	1,553	$	395	$	121