Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Summary of Assumptions Used in Black-Scholes Option Pricing Model

	Year Ended December 31,
	2023		2022		2021
Risk-free interest rate	3.38% - 4.65	%	1.70% - 4.21	%	0.66% - 1.41	%
Expected volatility	76.3% - 81.3	%	77.7% - 81.9	%	71.6% - 83.5	%
Expected dividend yield	0	%	0	%	0	%
Expected life of employee and Board options (in years)	6.25		6.25		6.25

Summary of Compensation Expense Relating to Stock Options

	Year Ended December 31,
	2023		2022		2021
Research and development	$	5,973	$	7,222	$	7,126
General and administrative		5,634		6,426		9,569
Total stock option expense	$	11,607	$	13,648	$	16,695

Summary of Stock Option Activity

A summary of the Company’s stock option activity related to employees, non-employee members of the Board of Directors and non-employee consultants for the 2019 Plan and the 2014 Plan as of and for the year ended December 31, 2023 is as follows:

		Weighted		Aggregate
	Number of	Average Exercise		Intrinsic
	Shares	Price		Value
Outstanding, December 31, 2022	7,689,449	$	14.35
Granted	2,004,668		8.15
Exercised	(93,218)		6.00
Forfeited	(286,035)		9.25
Expired	(1,417,217)		14.74
Outstanding, December 31, 2023	7,897,647	$	12.99	$	—
Weighted average remaining contractual life as of December 31, 2023 (in years)	6.71
Options exercisable, December 31, 2023	4,840,045	$	14.69	$	—
Weighted average remaining contractual life as of December 31, 2023 (in years)	5.46
Options vested and expected to vest as of December 31, 2023	7,897,647	$	12.99	$	—
Weighted average remaining contractual life as of December 31, 2023 (in years)	6.71

Employees And Non-Employee Members Of Board Of Directors [Member]

Summary of Restricted Stock Unit Activity

A summary of restricted stock unit activity related to employees and non-employee members of the Company’s Board of Directors as of and for the year ended December 31, 2023 is as follows:

		Weighted
	Number of	Average Grant
	Units	Date Fair Value
Outstanding, December 31, 2022	372,513	$	13.20
Awarded	601,172		7.81
Vested and released	(203,264)		12.46
Forfeited	(204,097)		8.96
Outstanding, December 31, 2023	566,324	$	9.27
Restricted stock units exercisable (vested and deferred), December 31, 2023	—