Stockholders' Equity Common Stock

6 Months Ended

Jun. 30, 2017

Equity [Abstract]

Stockholders' Equity Common Stock

8. Stockholders’ Equity Common Stock

Stock Options

The following table summarizes the Company’s stock option activity since December 31, 2016:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2016		5,069,133		$	14.36		8.26	$	16,736
Granted		1,609,500			10.07
Exercised		(56,282	)		0.65
Forfeited		(307,513	)		20.18
Outstanding as of June 30, 2017		6,314,838		$	13.11		8.15	$	20,875
Options exercisable as of June 30, 2017		2,800,162		$	11.10		7.34	$	14,634

The weighted average grant-date fair value of stock options granted during the three and six months ended June 30, 2017 and 2016 was $7.44, $6.98, $20.64, and $19.87 per share, respectively.

Restricted StockUnits

The Company has granted restricted stock units with time-based vesting conditions.  The table below summarizes the Company’s restricted stock activity for the six months ended June 30, 2017:

	Number of Shares			Weighted Average Grant Date Fair Value
Unvested restricted stock units as of December 31, 2016		115,500		$	9.78
Granted		332,500		$	10.08
Forfeited		(39,600	)	$	9.96
Vested		—		$	—
Unvested restricted stock units as of June 30, 2017		408,400		$	10.01

Stock-based Compensation Expense

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2017		2016		2017		2016
Research and development expenses	$	2,094	$	2,896	$	3,967	$	5,082
General and administrative expenses		2,409		1,821		4,814		3,539
	$	4,503	$	4,717	$	8,781	$	8,621