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Stock-based compensation - Plans narrative (Details) - shares
1 Months Ended 3 Months Ended
Jan. 01, 2022
Jun. 30, 2017
Mar. 31, 2022
Feb. 28, 2022
Dec. 31, 2021
Stock options          
Number of shares outstanding (in shares)     10,028,741   8,342,429
Stock options          
Stock options          
Vesting period     4 years    
2007 Plan          
Stock options          
Number of shares outstanding (in shares)   3,141,625      
2017 Plan          
Stock options          
Number of shares authorized (in shares)   2,255,000      
Cumulative annual increase in number of shares issuable   4.00%      
Additional shares authorized (in shares) 2,948,362        
Number of shares available for future issuance (in shares)     1,737,277    
Number of options granted in period (in shares)     2,788,158    
2017 Plan | Maximum          
Stock options          
Expiration period     10 years    
Inducement Award Program          
Stock options          
Number of shares outstanding (in shares)     757,500    
Number of shares authorized (in shares)       2,000,000