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Stock-based Compensation (Tables)
 9 Months Ended
Sep. 30, 2023
Share-Based Payment Arrangement [Abstract]  
Schedule of Stock-based Compensation Expense by Classification
Stock-based compensation expense by classification included within the Condensed Consolidated Statements of Operations and Comprehensive Loss was as follows (in thousands):
Three Months Ended
September 30,		Nine Months Ended
September 30,
2023202220232022
Research and development$4,548 $4,442 $14,439 $12,401 
General and administrative5,968 14,681 24,182 51,160 
Total stock-based compensation expense$10,516 $19,123 $38,621 $63,561 
Schedule of RSU Activity
A summary of the Company’s RSU activity was as follows:
Restricted Stock Units OutstandingWeighted-Average
Value at Grant
Date Per Share
Unvested RSUs as of December 31, 2022
872,077 $5.98 
RSUs granted2,559,677 $2.24 
RSUs vested(414,018)$3.89 
RSUs forfeited or canceled(240,673)$3.66 
Unvested RSUs as of September 30, 2023
2,777,063 $3.04 
Schedule of Stock Option Activity
A summary of the Company’s stock option activity was as follows:
Number of
Stock Options
Weighted-
Average
Exercise Price
Per Share		Weighted-
Average
Remaining
Contractual Life
(in years)		Aggregate
Intrinsic
Value
(in thousands)
Options outstanding as of December 31, 2022
53,849,045$5.09 7.84$24,887 
Granted12,276,063$2.30 
Exercised(1,478,537)$0.10 
Canceled or forfeited(4,196,756)$5.26 
Options outstanding as of September 30, 2023
60,449,815$4.63 7.58$7,517 
Options exercisable as of September 30, 2023
32,422,027$4.90 6.47$7,517 
Schedule of Assumptions Used in Black-Scholes Option-Pricing Model for Estimating Fair Value of Stock Options Granted
The fair value of stock options granted to employees, directors and consultants was estimated on the date of grant using the Black-Scholes option pricing model using the following weighted-average assumptions:
Nine Months Ended
September 30,
20232022
Risk-free interest rate4.13 %2.32 %
Expected volatility88.2 %85.6 %
Expected term (in years)6.065.98
Expected dividend yield0 %0 %