Stock Incentive Plans (Tables)

6 Months Ended

Jun. 30, 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 June 30,		Six months ended June 30,
	2022	2021	2022	2021
Expected volatility	69.3% - 69.6%	64.6% - 66.9%	68.7% - 69.6%	64.6% - 67.1%
Weighted-average risk-free interest rate	2.67% - 3.38%	0.90% - 1.20%	1.46% - 3.38%	0.50% - 1.20%
Expected dividend yield	— %	— %	— %	— %
Expected term (in years)	5.5 - 6.25	5.5 - 6.25	5.5 - 6.25	5.5 - 6.25
Underlying common stock fair value	$1.78-$2.88	$6.53-$9.62	$1.78-$4.17	$6.53-$13.91

Summary of Option Activity under Plans

The following table summarizes the Company’s stock option activity for the six months ended June 30, 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		2,844,380		$	2.71
Exercised		(293	)	$	2.71
Cancelled/Forfeited		(491,937	)	$	11.30
Outstanding at June 30, 2022		9,976,456		$	11.10		7.6	$	982
Vested and expected to vest at    June 30, 2022		9,976,456		$	11.10		7.6	$	982
Exercisable at June 30, 2022		5,355,617		$	13.35		6.5	$	948

Summary of Company's RSU Activity

The following table summarizes the Company’s RSU activity for the six months ended June 30, 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		(36,758	)	$	7.33
Outstanding at June 30, 2022		570,197		$	6.13

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 June 30,				Six months ended June 30,
	2022		2021		2022		2021
	(in thousands)
Research and development	$	1,088	$	2,303	$	3,254	$	4,159
General and administrative		2,055		2,170		3,940		4,197
	$	3,143	$	4,473	$	7,194	$	8,356