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Stock-based awards (Tables)
9 Months Ended
Sep. 30, 2021
Stock-based awards  
Schedule of assumptions used to determine grant-date fair value of stock options granted

Three Months Ended September 30, 

Nine Months Ended September 30, 

    

2021

2020

2021

2020

Expected term (in years)

 

5.96

 

n/a

5.89

5.81

Expected volatility

 

70.04

%

n/a

70.34

%

77.70

%

Weighted average risk-free interest rate

 

0.91

%

n/a

0.82

%

1.07

%

Expected dividend yield

 

0.00

%

n/a

0.00

%

0.00

%

Summary of stock option activity

    

    

Weighted-

    

Weighted-

    

Average

Average

Aggregate

Exercise

remaining

Intrinsic

Number

Price per

contractual

Value

of Options

Share

term (years)

(000's)

Balance outstanding, December 31, 2020

3,733,312

$

12.15

8.53

$

52,498

Options granted

422,263

$

25.71

Options exercised

(123,523)

$

5.15

Balance outstanding, September 30, 2021

4,032,052

$

13.79

7.98

$

39,854

Exercisable, September 30, 2021

 

1,843,127

$

10.20

7.63

$

23,444

Vested and expected to vest, September 30, 2021

 

4,032,052

$

13.79

7.98

$

39,854

Summary of stock-based compensation expense

Three Months Ended September 30, 

Nine Months Ended September 30, 

2021

2020

2021

2020

Classified within research and development expense

$

770

$

378

$

2,223

$

1,115

Classified within general and administrative expense

1,842

1,168

5,189

2,991

Total stock-based compensation expense

$

2,612

$

1,546

$

7,412

$

4,106