Stock Incentive Plans (Tables)

9 Months Ended

Sep. 30, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of Stock Options Valuation Assumptions Using a Black-Scholes Option Pricing Model

The assumptions used in the Black-Scholes option pricing model are as follows (note that there were no options granted during the three months ended September 30, 2023):

	Three months ended	Nine months ended September 30,
	September 30, 2022	2023	2022
Expected volatility	70.1%	69.2% - 69.7%	68.7% - 70.1%
Weighted-average risk-free interest rate	3.20% - 3.66%	3.45% - 4.22%	1.46% - 3.66%
Expected dividend yield	— %	— %	— %
Expected term (in years)	6.25	5.5 - 6.25	5.5 - 6.25
Underlying common stock fair value	$1.82-$2.82	$0.92-$1.60	$1.78-$4.17

Summary of Option Activity under Plans

The following table summarizes the Company’s stock option activity for the nine months ended September 30, 2023:

	Number of Options			Weighted- Average Exercise Price per Share		Weighted- Average Remaining Contractual Term (in Years)		Aggregate Intrinsic Value
								(in thousands)
Outstanding at January 1, 2023		9,865,734		$	10.96		7.2	$	493
Granted		3,188,150		$	1.53
Exercised		(3,366	)	$	0.47
Cancelled/Forfeited		(623,776	)	$	11.11
Outstanding at September 30, 2023		12,426,742		$	8.55		4.9	$	488
Vested and expected to vest at    September 30, 2023		12,426,742		$	8.55		4.9	$	488
Exercisable at September 30, 2023		7,566,304		$	11.80		4.5	$	421

Summary of Company's RSU Activity

The following table summarizes the Company's RSU activity for the nine months ended September 30, 2023:

	Number of Restricted Stock Units			Weighted- Average Grant Date Fair Value
Outstanding at January 1, 2023		543,179		$	6.12
Granted		483,850		$	1.60
Vested		(281,117	)	$	5.31
Forfeited		(258,184	)	$	2.54
Outstanding at September 30, 2023		487,728		$	3.04

Schedule of Stock-Based Compensation Expense

The Company recorded stock-based compensation expense related to stock options, shares purchased under the 2018 ESPP, restricted stock units and stock award modifications as follows:

	Three months ended September 30,				Nine months ended September 30,
	2023		2022		2023		2022
	(in thousands)
Research and development	$	230	$	889	$	1,507	$	4,143
General and administrative		1,477		1,882		4,970		5,822
	$	1,707	$	2,771	$	6,477	$	9,965