Stockholders' Equity Common Stock (Tables)

9 Months Ended

Sep. 30, 2018

Equity [Abstract]

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity since December 31, 2017:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2017		6,125,692		$	13.00		7.70	$	15,808
Granted		1,820,776			10.08
Exercised		(196,508	)		0.69
Forfeited		(305,920	)		16.96
Outstanding as of September 30, 2018		7,444,040		$	12.45		7.55	$	9,360,614
Options vested and expected to vest as of September    30, 2018		7,444,040			12.45		7.55		9,360,614
Options exercisable as of September 30, 2018		4,176,275		$	12.23		6.61	$	9,357,014

Summary of Restricted Stock Unit Activity

The Company has granted restricted stock units with time-based vesting conditions.  The table below summarizes the Company’s restricted stock unit activity since December 31, 2017:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2017		356,778		$	10.01
Granted		2,000		$	7.43
Forfeited		(7,370	)	$	9.78
Vested		(61,500	)	$	10.12
Unvested restricted stock units as of September 30, 2018		289,908		$	9.98

Summary of Stock Based Compensation Expense

The Company recorded stock-based compensation expense related to stock options, restricted stock units and the Company’s Employee Stock purchase Plan (“ESPP”) in the following expense categories of its condensed consolidated statements of operations and comprehensive loss:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Research and development expenses	$	2,246	$	2,158	$	6,436	$	6,124
General and administrative expenses		2,071		2,211		6,451		7,026
	$	4,317	$	4,369	$	12,887	$	13,150