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Stock-Based Awards (Tables)
 12 Months Ended
Dec. 31, 2021
Share-based Payment Arrangement [Abstract]  
Summary of Assumptions used to Determine Fair Value of Stock Options Granted to Employees and Directors
The assumptions that the Company used to determine the fair value of the stock options granted to employees and directors were as follows, presented on a weighted average basis:
 Year Ended December 31,
 202120202019
Risk-free interest rate0.89 %1.29 %2.46 %
Expected term (in years)5.965.996.12
Expected volatility83.87 %71.34 %73.62 %
Expected dividend yield0.0 %0.0 %0.0 %
Summary of Stock Option Activity
The following table summarizes the Company’s stock option activity for the year ended December 31, 2021:
 Number of
Shares		Weighted
Average
Exercise
Price		Weighted
Average
Remaining
Contractual
Term		Aggregate
Intrinsic
Value
 (in years)
Outstanding as of December 31, 20206,011,126 $5.55 7.28$24,912 
Granted1,838,905 9.11 
Exercised(508,720)3.98 
Forfeited(284,053)5.56 
Outstanding as of December 31, 20217,057,258 $6.59 6.98$4,678 
Options exercisable at December 31, 20214,678,355 $6.22 6.13$3,683 
Vested and expected to vest at December 31, 20217,057,258 $6.59 6.98$4,678 
Summary of Restricted Stock Unit Activity
The table below summarizes the Company’s restricted stock unit activity since December 31, 2020:
Number of
Shares		Weighted Average
Grant-Date Fair Value
Unvested restricted stock units as of December 31, 20201,043,300 $3.21 
Granted— — 
Vested(997,400)3.21 
Forfeited(45,900)3.18 
Unvested restricted stock units as of December 31, 2021— $— 
Summary of Stock-Based Compensation Expense Related to Stock Options, Restricted Stock Awards and ESPP
The Company recorded stock-based compensation expense related to stock options, restricted stock awards, and the ESPP in the following expense categories of its statements of operations and comprehensive loss:
 
 Year Ended December 31,
 202120202019
Research and development expenses$2,431 $2,826 $2,350 
General and administrative expenses6,115 4,939 3,641 
 $8,546 $7,765 $5,991