Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2023

Equity [Abstract]

Schedule of Activity under 2008 Plan and 2018 Plan

The following is a summary of the activity under the Company's equity incentive plans:

	Outstanding Options			Weighted Average Remaining Contractual Life (In Years)	Aggregate Intrinsic Value (In Thousands)
	Number of Options (In Thousands)	Weighted Average Exercise Price
Balances at December 31, 2022	14,215	$	14.74	6.89	$	1,749
Options granted	5,029	4.32
Options exercised	(351)	1.90
Options forfeited	(2,494)	11.42
Options expired	(375)	14.80
Balances at June 30, 2023	16,024	$	12.27	6.24	$	40
Vested and expected to vest at June 30, 2023	15,556	$	12.35	6.16	$	40
Exercisable at June 30, 2023	9,303	$	14.51	4.14	$	40

Schedule of Stock Based Compensation Expense

Stock-based compensation expense was allocated as follows (in thousands):

	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
Research and development	$	3,586	$	4,411	$	8,400	$	8,622
General and administrative	3,890		3,691		7,613		7,300
Total stock-based compensation expense	$	7,476	$	8,102	$	16,013	$	15,922