Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Company's Option Activity

The following is a summary of stock option activity for the three months ended September 30, 2019,

				Weighted		Weighted
				Average		Average		Aggregate
	Number			Exercise		Contractual		Intrinsic
	of Shares			Price		Term		Value
						(in years)		(in thousands)
Outstanding as of December 31, 2018		3,779,403		$	7.78		8.80	$	110
Granted		1,397,699			9.06
Exercised		(23,906	)		5.54
Forfeited		(280,099	)		9.15
Outstanding as of September 30, 2019		4,873,097		$	8.07		8.44	$	1,575
Vested and expected to vest as of September 30,    2019		4,873,097		$	8.07		8.44	$	1,575
Options exercisable as of September 30, 2019		1,714,765		$	7.08		7.68	$	1,043

Schedule of Weighted Average Basis Assumptions Used in Black-Scholes Option-Pricing Model

The Company estimated the fair value of each stock option award using the Black-Scholes option-pricing model based on the following assumptions:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2019			2018			2019			2018
Risk-free interest rate		1.58	%		2.76	%		2.36	%		2.77	%
Expected volatility		82.22	%		81.14	%		82.24	%		80.96	%
Expected dividend yield		—			—			—			—
Expected term (in years)		6.10			6.05			6.03			6.05

Schedule of Stock Based Compensation Expense Related to Statements of Operations and Comprehensive Loss

The Company recorded stock-based compensation expense in the following expense categories of its statements of operations and comprehensive loss (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
Research and development expenses	$	744	$	566	$	2,000	$	1,068
General and administrative expenses		1,204		678		3,058		1,448
Total	$	1,948	$	1,244	$	5,058	$	2,516