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Equity (Tables)
 9 Months Ended
Sep. 30, 2021
Equity [Abstract]  
Summary of Stock-based Compensation Expense
Stock-based compensation expense is classified in the condensed consolidated statement of operations as follows:
(in thousands)Three Months Ended
September 30,		Nine Months Ended
September 30,
2021202020212020
Research and development expenses$1,423 $571 $3,850 $1,200 
General and administrative expenses1,787 1,117 4,698 2,193 
Total stock-based compensation expense$3,210 $1,688 $8,548 $3,393 
Schedule of Weighted Average Assumptions
The fair values of stock options granted are estimated using the Black-Scholes option pricing model with the following weighted average assumptions:
 Three Months Ended
September 30,		Nine Months Ended
September 30,
 2021202020212020
Expected volatility89.17 %94.84 %89.18 %93.86 %
Expected dividends0 %0 %0 %0 %
Expected terms (years)6.076.076.036.02
Risk free rate0.83 %0.34 %0.89 %0.42 %
Schedule of Stock Option Activity
A summary of the Company’s stock option activity and related information for the nine months ended September 30, 2021 is as follows:
 Number of SharesWeighted Average Exercise PriceWeighted Average Remaining Contractual Life
 (in Years)		Aggregate Intrinsic Value
(in Thousands)
Outstanding at December 31, 20206,846,289 $6.42 8.71$53,127 
Options granted3,019,749 $8.85 
Options exercised(124,366)$3.28 
Options cancelled/forfeited(122,534)$11.14 
Outstanding at September 30, 20219,619,138 $7.16 8.53$18,377 
Exercisable as of September 30, 20213,134,157 $5.90 7.58$9,339 
Summary of RSU Activity
A summary of the Company’s RSU activity and related information for the nine months ended September 30, 2021 is as follows:
 Number of SharesWeighted Average Grant Date Fair Value
Non-vested at December 31, 2020186,500 $8.19 
Restricted stock units granted70,000 $12.94 
Restricted stock units vested(84,500)$7.20 
Restricted stock units forfeited(1,500)$12.00 
Non-vested at September 30, 2021170,500 $10.59