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Stock-based compensation - Summary of incentive plan for members of management (Details) - Performance Based Shares - $ / shares
3 Months Ended 12 Months Ended
Mar. 31, 2022
Dec. 31, 2021
Restricted Stock    
Non-vested at beginning of period 321,883 358,512
Granted 109,441 191,479
Performance Shares Quantity Adjustment 20,608 54,306
Vested (169,260) (273,974)
Forfeited   (8,440)
Non-vested at end of period 282,672 321,883
Weighted-Average Grant Date Fair Value    
Non-vested at beginning of period $ 47.98 $ 41.23
Granted 87.10 69.38
Performance Shares Quantity Adjustment 77.65 54.21
Vested 71.47 55.11
Forfeited   43.48
Non-vested at end of period $ 51.23 $ 47.98