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Stock-based compensation - Unrecognized expense and weighted-average period (Details) - $ / shares
12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Fair value assumptions      
Expected dividend yield 0.00%    
Stock options      
Options disclosures      
Weighted average fair value of grants (in dollars per share) $ 3.60    
Employees and directors stock options      
Fair value assumptions      
Risk-free interest rate 2.20% 0.90% 1.00%
Expected term 6 years 6 years 6 years
Expected volatility 79.40% 75.00% 73.70%