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Stock-Based Compensation (Tables)
12 Months Ended
Dec. 31, 2023
Share-Based Payment Arrangement [Abstract]  
Schedule of Stock-Based Compensation Expenses Related to Statement of Operations
The following table presents stock-based compensation included on the consolidated statements of operations (in thousands):
Year Ended December 31,
202320222021
Stock-based compensation expense:
Stock options$13,884 $13,280 $11,623 
RSUs35,279 26,899 45,558 
$49,163 $40,179 $57,181 
Stock-based compensation expense in operating expenses:
Research and development$17,341 $11,669 $18,819 
Selling, general and administrative31,822 28,510 38,362 
$49,163 $40,179 $57,181 
Schedule of Stock Option Activity and Related Information under Equity Plans
The following table summarizes stock option activity and related information for the year ended December 31, 2023:
 
Number of
Options
Weighted-
Average
Exercise
Price
Aggregate
Intrinsic
Value
(in thousands)
Weighted-
Average
Remaining
Contractual
Life
(in years)
Outstanding as of December 31, 2022
9,262,926 $9.87 $4,848 7.2
Granted949,578 $2.99 
Exercised(184,362)$1.59 
Expired/forfeited(207,707)$5.53 
Outstanding as of December 31, 2023
9,820,435 $9.46 $6,046 6.6
Vested and exercisable as of December 31, 2023
5,867,252 $11.54 $4,118 5.4
Schedule of Weighted Average Fair Value of Options Under Black-Scholes Option Pricing Model
The fair value of stock options issued was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:
Year Ended December 31,
202320222021
Expected term5.50 years5.69 years5.90 years
Risk-free interest rate4.0 %2.6 %0.7 %
Expected volatility116.2 %101.8 %101.0 %
Dividend yield— %— %— %
Weighted-average grant date fair value$2.53$4.20$16.80
Schedule of RSU Activity under Equity Plans
The following table summarizes RSU activity during the year ended December 31, 2023:
Number of
Units
Weighted-
Average
Grant Date
Fair Value
Nonvested balance as of December 31, 2022
6,551,388 $18.27 
Granted6,407,432 $1.72 
Vested(4,545,644)$7.33 
Forfeited/canceled(909,197)$7.99 
Nonvested balance as of December 31, 2023
7,503,979 $12.01