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Equity Incentive Plans (Tables)
12 Months Ended
Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]  
Schedule of Activity Related to Stock Option Awards A summary of the activity related to stock option awards during the year ended December 31, 2023 is as follows:
Shares
Subject to
Options
Weighted-Average
Exercise
Price per
Share
Weighted-Average
Remaining
Contractual
Term (in years)
Aggregate
Intrinsic
Value (in
thousands)
Outstanding at January 1, 20233,673,208 $32.04 6.28$18,686 
Granted1,579,331 $22.02 
Exercises(90,883)$18.95 
Forfeitures and cancellations(936,041)$37.52 
Outstanding at December 31, 2023
4,225,615 $27.36 7.42$5,827 
Exercisable at December 31, 20232,154,408 $30.60 6.10$4,741 
Schedule of Time-based Restricted Stock Units Activity
Number of Restricted Stock UnitsWeighted-Average Grant Date Fair Value
Weighted-Average
Remaining
Contractual
Term
(in years)
Aggregate
Intrinsic
Value (in
thousands)
Outstanding at January 1, 20231,028,843 $26.14 1.17$31,884 
Granted568,574 $22.02 
Released(68,900)$23.89 
Forfeitures and cancellations(46,945)$21.87 
Outstanding at December 31, 20231,481,572 $24.80 0.73$31,735 
RSU expected to vest at December 31, 20231,481,572 $24.80 0.73$31,735 
Schedule of Weighted Average Assumptions in Stock Option Valuations The
estimated fair values of stock option awards granted were determined on the date of grant using the Black-Scholes option valuation model with the following weighted-average assumptions:
Year Ended
December 31,
202320222021
Risk-free interest rate3.8 %2.5 %0.7 %
Expected volatility85.7 %87.4 %92.9 %
Expected dividend yield— %— %— %
Expected term (in years)5.826.096.18
Weighted average grant date fair value per share$16.06$21.58$22.34
Schedule of Non-cash Stock-based Compensation Expense
Total non-cash stock-based compensation expense for all stock awards that was recognized in the consolidated statements of operations and comprehensive loss is as follows:
Year Ended
December 31,
(in thousands)202320222021
Research and development$10,159 $6,775 $5,856 
General and administrative23,046 20,581 9,491 
Total
$33,205 $27,356 $15,347