Share-Based Compensation - (Tables)

6 Months Ended

Jun. 30, 2019

Share-based Payment Arrangement [Abstract]

Schedule of Allocation of Share-based Compensation Costs by Award Type

Share-based compensation expense, net of estimated forfeitures, includes expenses related to stock options and RSUs granted to employees, non-employee directors and consultants, as well as options granted to employees to purchase shares under the ESPP. Stock-based compensation by award type was as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Stock options	$	1,488	$	1,836	$	3,110	$	3,968
Restricted stock units	709		819		1,530		1,765
Employee stock purchase plan	10		7		37		11
Total	$	2,207	$	2,662	$	4,677	$	5,744

Schedule of Allocation of Share-based Compensation Costs by Financial Statement Line

The Company allocated stock-based compensation expense in the Company’s Consolidated Statements of Operations and Comprehensive Loss as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
	2019		2018		2019		2018
Research and development	$	989	$	1,106	$	2,159	$	2,546
General and administrative	1,218		1,556		2,518		3,198
Total	$	2,207	$	2,662	$	4,677	$	5,744

Summary of the stock option activity including weighted average exercise prices, options outstanding and exercisable

A summary of the stock option activity, weighted average exercise prices, options outstanding, exercisable and expected to vest as of June 30, 2019 is as follows (in thousands except weighted average exercise price):

	Number of Shares Underlying Options		Weighted Average Exercise Price
Outstanding, December 31, 2018	5,903		$	13.72
Granted	137		$	1.35
Forfeited	(261	)	$	26.18
Expired	(89	)	$	12.72
Outstanding, June 30, 2019	5,690		$	12.89
Vested and exercisable, June 30, 2019	2,850		$	21.83
Vested and expected to vest, June 30, 2019	5,463		$	13.26

Summary of the Company's outstanding shares of RSU awards

The following table presents a summary of the Company's outstanding RSU awards granted as of June 30, 2019 (in thousands except weighted average grant-date fair value):

	Restricted Stock Units		Weighted Average Grant-Date Fair Value
Outstanding, December 31, 2018	679		$	15.61
Awarded	10		$	1.38
Vested	(49	)	$	52.83
Forfeited	(5	)	$	38.98
Outstanding, June 30, 2019	635		$	12.40
Outstanding, Expected to vest	518		$	6.58