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Stock-based compensation - Summary of incentive plan for members of management (Details) - Performance Based Shares - $ / shares
12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Restricted Stock      
Non-vested at beginning of period 281,963 321,883 358,512
Granted 257,757 194,791 191,479
Performance Shares Quantity Adjustment 19,753 6,947 54,306
Vested (243,133) (240,033) (273,974)
Forfeited (16,444) (1,625) (8,440)
Non-vested at end of period 299,896 281,963 321,883
Weighted-Average Grant Date Fair Value      
Non-vested at beginning of period $ 56.50 $ 47.98 $ 41.23
Granted 66.01 84.29 69.38
Performance Shares Quantity Adjustment 75.32 78.02 54.21
Vested 66.31 66.11 55.11
Forfeited 55.82 78.86 43.48
Non-vested at end of period $ 58.20 $ 56.50 $ 47.98