Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2022

Summary of Assumptions Used in Black-Scholes Option Pricing Model

	Year Ended December 31,
	2022		2021		2020
Risk-free interest rate	1.70% - 4.21	%	0.66% - 1.41	%	0.35% - 1.57	%
Expected volatility	77.7% - 81.9	%	71.6% - 83.5	%	71.8% - 74.8	%
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,
	2022		2021		2020
Research and development	$	7,222	$	7,126	$	6,765
General and administrative		6,426		9,569		4,943
Total stock option expense	$	13,648	$	16,695	$	11,708

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, 2022 is as follows:

		Weighted		Aggregate
	Number of	Average Exercise		Intrinsic
	Shares	Price		Value
Outstanding, December 31, 2021	6,512,280	$	15.58
Granted	1,899,919		10.25
Exercised	(48,307)		6.43
Forfeited	(356,819)		14.50
Expired	(317,624)		16.09
Outstanding, December 31, 2022	7,689,449	$	14.35	$	3,028
Weighted average remaining contractual life as of December 31, 2022 (in years)	5.95
Options exercisable, December 31, 2022	4,972,944	$	15.06	$	1,940
Weighted average remaining contractual life as of December 31, 2022 (in years)	4.40
Options vested and expected to vest as of December 31, 2022	7,689,449	$	14.35	$	3,028
Weighted average remaining contractual life as of December 31, 2022 (in years)	5.95

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, 2022 is as follows:

		Weighted
	Number of	Average Grant
	Units	Date Fair Value
Outstanding, December 31, 2021	576,544	$	17.50
Awarded	474,193		10.10
Vested and released	(268,222)		16.33
Forfeited	(410,002)		13.62
Outstanding, December 31, 2022	372,513	$	13.20
Restricted stock units exercisable (vested and deferred), December 31, 2022	—