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Stock-based awards (Tables)
12 Months Ended
Dec. 31, 2021
Stock-based awards  
Schedule of assumptions used to determine grant-date fair value of stock options granted

Year Ended December 31, 

2021

2020

2019

Expected term (in years)

5.77

6.00

6.00

Expected volatility

72.17

%

73.38

%

73.75

%

Weighted average risk-free interest rate

1.19

%

0.65

%

2.12

%

Expected dividend yield

0.00

%

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

1,648,855

$

22.29

Options exercised

(140,128)

$

5.36

Options cancelled

(20,945)

$

23.91

Balance outstanding, December 31, 2021

5,221,094

$

15.49

8.20

$

36,168

Vested and expected to vest, December 31, 2021

 

4,610,548

$

14.75

 

7.97

$

36,137

Exercisable, December 31, 2021

 

2,115,158

$

10.45

 

7.29

$

24,365

Summary of stock-based compensation expense

Year Ended December 31, 

2021

2020

2019

Classified within research and development expense

$

3,054

$

1,633

$

485

Classified within general and administrative expense

7,000

4,389

1,285

Total stock-based compensation expense

$

10,054

$

6,022

$

1,770