Share-Based Payments (Tables)

6 Months Ended

Jun. 30, 2018

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

Summary of Stock-Based Compensation Expense

Stock-based compensation expense by award type was as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Stock options	$	283	$	268	$	659	$	455
Restricted stock	—		51		$	22	102
Restricted stock units	—		—		$	—	3
Employee stock purchase plan	2		3		5		6
	$	285	$	322	$	686	$	566

The Company allocated stock-based compensation expense as follows in the condensed consolidated statements of operations and comprehensive loss (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2018		2017		2018		2017
Research and development expense	$	123	$	83	$	288	$	123
General and administrative expense	162		239		$	398	$	443
	$	285	$	322	$	686	$	566

Summary of Stock Option Activity and Related Information

A summary of the stock option activity is presented below:

	Shares		Weighted-Average Exercise Price
Outstanding at December 31, 2017	2,695,796		$	3.16
Granted	1,643,400		1.82
Exercised	(55,259	)	0.53
Cancelled or forfeited	(256,111	)	2.95
Outstanding at June 30, 2018	4,027,826		$	2.66
Exercisable at June 30, 2018	1,738,331		$	3.53
Vested and expected to vest at June 30, 2018(1)	3,977,226		$	2.67

⁽¹⁾  Represents the number of vested stock options, plus the number of unvested stock options expected to vest. The Company adopted ASU 2016-09 as of January 1, 2017 and records forfeitures as they occur.

Summary of Restricted Stock

A summary of the restricted stock is presented below:

	Restricted Stock		Weighted-Average Grant Date Fair Value
Unvested at December 31, 2017	4,430		$	11.43
Vested	(4,430	)	11.43
Unvested at June 30, 2018	—