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Share-based payment - Weighted average assumptions (Details)
12 Months Ended
Dec. 31, 2021
USD ($)
yr
Dec. 31, 2020
USD ($)
yr
Dec. 31, 2019
USD ($)
yr
Weighted average assumptions [Abstract]      
Expected volatility 41.05% 41.25% 35.68%
Expected terms (in years) | yr 6.16 6.11 5.81
Risk-free interest rate 1.06% 0.53% 1.85%
Expected dividend yield $ 0 $ 0 $ 0
Grant date fair value $ 1.87 $ 1.72 $ 2.23