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Share-based compensation - Fair value measurement (Details)
12 Months Ended
Dec. 31, 2022
USD ($)
Y
$ / shares
Dec. 31, 2021
USD ($)
Y
$ / shares
Dec. 31, 2020
USD ($)
Y
$ / shares
NL & US      
Share-based compensation      
Expected annual volatility 83.90%    
Expected life, years | Y 6.08    
Weighted average grant date fair value | $ $ 4.01    
NL & US | Bottom of range      
Share-based compensation      
Fair value of the common share $ 1.71    
Exercise price $ 2.34    
Risk-free interest rate 1.65%    
NL & US | Top of range      
Share-based compensation      
Fair value of the common share $ 3.91    
Exercise price $ 5.50    
Risk-free interest rate 3.78%    
NL      
Share-based compensation      
Expected annual volatility   80.10%  
Expected life, years | Y   6.08 3.92
Exercise price     $ 0
Risk-free interest rate     0.62%
Weighted average grant date fair value | $   $ 3.61 $ 2.71
NL | Bottom of range      
Share-based compensation      
Expected annual volatility     75.50%
Fair value of the common share   $ 3.42 $ 2.10
Exercise price   $ 5.10  
Risk-free interest rate   0.30%  
NL | Top of range      
Share-based compensation      
Expected annual volatility     90.00%
Fair value of the common share   $ 5.23 $ 2.76
Exercise price   $ 7.77  
Risk-free interest rate   0.53%  
US      
Share-based compensation      
Expected annual volatility   80.10%  
Expected life, years | Y   6.08  
Weighted average grant date fair value | $   $ 5.95  
US | Bottom of range      
Share-based compensation      
Fair value of the common share   $ 3.12  
Exercise price   $ 5.10  
Risk-free interest rate   0.94%  
US | Top of range      
Share-based compensation      
Fair value of the common share   $ 8.71  
Exercise price   $ 15.00  
Risk-free interest rate   1.34%