Stock-Based Awards (Tables)

12 Months Ended

Dec. 31, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Assumptions used to Determine Fair Value of Stock Options Granted to Employees and Directors

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,
	2019			2018			2017
Risk-free interest rate		2.46	%		2.67	%		2.04	%
Expected term (in years)		6.12			6.18			6.25
Expected volatility		73.62	%		72.70	%		78.60	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

Summary of Stock Option Activity

The following table summarizes the Company’s stock option activity for the year ended December 31, 2019:

	Number of Shares			Weighted Average Exercise Price		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(in years)
Outstanding as of December 31, 2018		4,414,225		$	6.79		8.29	$	2,031
Granted		1,518,500			4.06
Exercised		(110,156	)		2.31
Forfeited		(404,456	)		6.85
Outstanding as of December 31, 2019		5,418,113		$	6.11		7.69	$	690
Options exercisable at December 31, 2019		2,919,360		$	5.54		7.02	$	665
Vested and expected to vest at December 31, 2019		5,418,113		$	6.11		7.69	$	690

Summary of Stock-Based Compensation Expense Related to Stock Options, Restricted Stock Awards and ESPP

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

	Year Ended December 31,
	2019		2018		2017
Research and development expenses	$	2,350	$	2,557	$	1,917
General and administrative expenses		3,641		2,660		2,792
	$	5,991	$	5,217	$	4,709