Stock-Based Compensation (Tables)
 12 Months Ended
Dec. 31, 2022
Share-Based Payment Arrangement [Abstract]  
Schedule of assumptions used to determine the fair value of stock awards granted
The following table presents, on a weighted average basis, the assumptions used in the Black-Scholes option-pricing model to determine the fair value of stock-based awards granted to employees, directors, and non-employees:
Year ended December 31,
202220212020
Risk-free interest rate2.37 %0.81 %1.10 %
Expected volatility78.4 %77.4 %69.4 %
Expected dividend yield———
Expected term (in years)5.876.086.05
Schedule of stock option activity
The following table summarizes the Company’s service-based and performance-based option activity since December 31, 2022:

Number of
shares		Weighted average exercise
price		Weighted average contractual termAggregate intrinsic
value
(in years)(in thousands)
Outstanding as of December 31, 202117,138,772$12.047.22$23,511
Granted4,104,4034.37  
Exercised(42,228)2.32  
Forfeited(7,105,039)10.31  
Outstanding as of December 31, 202214,095,908$10.713.55$6
Vested and expected to vest as of December 31, 202214,095,908$10.713.55$6
Options exercisable as of December 31, 202212,061,182$11.292.82$6
Schedule of restricted stock unit activity The following table summarizes the Company’s restricted stock unit activity since December 31, 2022:
SharesWeighted average
grant-date
fair value
Unvested restricted common stock as of December 31, 2021794,244$15.346
Issued906,8154.880
Vested(137,828)12.522
Forfeited(1,130,028)9.446
Unvested restricted common stock as of December 31, 2022433,203$9.728
Schedule of allocation of share based compensation
The Company recorded stock-based compensation expense in the following expense categories of its consolidated statements of operations and comprehensive loss (in thousands):
Year ended December 31,
202220212020
Research and development expenses$6,863 $12,338 $8,023 
General and administrative expenses8,920 23,272 25,642 
$15,783 $35,610 $33,665