Stockholders’ Equity (Deficit) Common Stock (Tables)

12 Months Ended

Dec. 31, 2015

Equity [Abstract]

Summary of Fair Value of Stock Option

The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors were as follows, presented on a weighted average basis:

	Year Ended December 31,
	2015			2014			2013
Risk-free interest rate		1.80	%		1.83	%		1.27	%
Expected term (in years)		6.0			6.0			6.0
Expected volatility		81.4	%		83.5	%		85.9	%
Expected dividend yield		0	%		0	%		0	%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the twelve months ended December 31, 2015:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2014		3,579,342		$	1.38		9.21	$	59,498
Granted		1,750,124			20.44
Exercised		(232,970	)		0.40
Forfeited		(70,250	)		5.04
Outstanding as of December 31, 2015		5,026,246		$	8.01		8.70	$	136,945
Options vested and expected to vest as of December 31, 2015		5,026,246		$	8.01		8.70	$	136,945
Options exercisable as of December 31, 2015		1,643,955		$	1.33	8.13		$	55,507

Summary of Restricted Stock Activity

The table below summarizes the Company’s restricted stock activity for the twelve months ended December 31, 2015:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted common stock as of December 31, 2014		52,500		$	0.001
Vested		(52,500	)	$	0.001
Unvested restricted common stock as of December 31, 2015		—		$	0.001

Summary of Stock Based Compensation Expense

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

	Year Ended December 31,
	2015		2014		2013
Research and development expenses	$	5,297	$	1,068	$	177
General and administrative expenses		4,397		1,000		32
	$	9,694	$	2,068	$	209