Stock Incentive Plans (Tables)

3 Months Ended

Mar. 31, 2022

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:

	Three months ended March 31,
	2022	2021
Expected volatility	68.7% - 69.5%	66.8% - 67.1%
Weighted-average risk-free interest rate	1.46% - 1.89%	0.50% - 0.76%
Expected dividend yield	— %	— %
Expected term (in years)	6.00 - 6.25	6.25
Underlying common stock fair value	$2.71-$4.17	$11.64-$13.91

Summary of Option Activity under Plans

The following table summarizes the Company’s stock option activity for the three months ended March 31, 2022:

	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, 2022		7,624,306		$	14.25		7.5	$	2,069
Granted		2,581,980		$	2.80
Exercised		(293	)	$	2.71
Cancelled/Forfeited		(199,264	)	$	12.31
Outstanding at March 31, 2022		10,006,729		$	11.33		7.8	$	2,415
Vested and expected to vest at    March 31, 2022		10,006,729		$	11.33		7.8	$	2,415
Exercisable at March 31, 2022		4,874,177		$	13.68		6.5	$	1,676

Summary of Company's RSU Activity

The following table summarizes the Company’s RSU activity for the three months ended March 31, 2022:

	Number of Restricted Stock Units			Weighted- Average Grant Date Fair Value
Outstanding at January 1, 2022		307,600		$	12.75
Granted		386,495		$	2.71
Vested		(87,140	)	$	13.85
Forfeited		(10,979	)	$	12.10
Outstanding at March 31, 2022		595,976		$	6.10

Schedule of Stock-Based Compensation Expense

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

	Three months ended March 31,
	2022		2021
	(in thousands)
Research and development	$	2,166	$	1,857
General and administrative		1,885		2,026
	$	4,051	$	3,883