Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of Stock-based Compensation Expense

Stock-based compensation expense was as follows:

	Years Ended December 31,
(in thousands)	2023		2022
Research and development	$	13,167	$	14,014
General and administrative		27,612		27,301
Total stock-based compensation expense	$	40,779	$	41,315

Summary of Restricted Common Stock Activity

The following table summarizes restricted common stock activity for the year ended December 31, 2023:

	Shares			Weighted Average Grant Date Fair Value
Unvested at January 1, 2023		2,239,106		$	13.75
Granted		2,279,994			6.02
Forfeited		(342,732	)		11.46
Vested		(921,505	)		13.24
Unvested at December 31, 2023		3,254,863		$	8.73

Summary of Stock Option Activity

The following table summarizes stock option activity (in thousands, except share and per share data):

	Shares			Weighted Average Exercise Price		Weighted Average Contractual Life		Aggregate Intrinsic Value
Options outstanding at January 1, 2023		7,922,797		$	17.81		8.3	$	786
Granted		3,779,342			6.24		—		57
Exercised		—			—		—		—
Forfeited		(1,262,388	)		16.25		—		82
Options outstanding at December 31, 2023		10,439,751		$	13.81		7.9	$	—
Options vested and exercisable at December 31, 2023		4,534,147		$	18.86		7.2	$	—

Schedule of Estimated Fair Value Weighted-Average Assumptions Using Black-Scholes Option-Pricing Model

The fair value was estimated on the date of grant using the Black-Scholes option-pricing model, with the following weighted-average assumptions:

	Years Ended December 31,
	2023			2022
Expected term (in years)		6.11			6.07
Expected volatility		94	%		90	%
Risk-free interest rate		3.52	%		2.00	%
Expected dividend yield	—				—
Fair value of common stock	$	6.24		$	7.48