Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity

The following tables summarize stock option activity under the 2017 Plan and the 2019 Plan:

	Number of Awards			Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (Years)		Aggregate Intrinsic Value
	(in thousands except share data)
Outstanding, December 31, 2019		5,681,422		$	3.60		8.6	$	69,219
Granted		1,207,300			16.61
Exercised		(106,683	)		1.29
Cancelled/Forfeited		(104,070	)		3.08
Outstanding, September 30, 2020		6,677,969		$	6.02		8.2	$	36,096
Exercisable, September 30, 2020		2,786,298			2.65		7.8		21,136
Vested and expected to vest, September 30, 2020		6,677,969			6.02		8.2		36,096

Schedule of Assumptions to Estimate Fair Value of Stock Options Using Black-Scholes Option Pricing Model

The weighted average fair value and assumptions used to determine the fair value of stock options granted was as follows:

	Three Months Ended September 30,						Nine Months Ended September 30,
	2020			2019			2020			2019
Grant date fair value	$	13.53		$	7.22		$	16.61		$	6.19
Expected term		5.9			6.0			6.0			6.0
Risk-free interest rate		0.4	%		1.4	%		1.2	%		2.4	%
Expected volatility		86.6	%		81.6	%		86.1	%		79.1	%
Dividend rate		—			—			—			—

Summary of Non-vested Restricted Stock Award Activity

The following table presents a summary of the Company’s non-vested restricted stock award activity under all plans and related information for the nine months ended September 30, 2020:

	Number of Restricted Stock Awards Outstanding			Weighted Average Grant Date Fair Value Per Share
Non-vested restricted stock awards outstanding as of December 31, 2019		978,759		$	0.18
Restricted stock awards vested		(440,433	)		0.18
Non-vested restricted stock awards outstanding as of September 30, 2020		538,326			0.18

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
	(in thousands)
Aggregate grant date fair value of restricted stock awards vested	$	25	$	25	$	76	$	76

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense is recognized for restricted stock and stock options granted to employees and non-employees and has been reported in the Company’s statements of operations and comprehensive loss as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2019		2020		2019
	(in thousands)
Research and development	$	1,079	$	676	$	3,014	$	1,741
General and administrative		1,398		620		3,344		1,276
Total stock-based compensation expense	$	2,477	$	1,296	$	6,358	$	3,017