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Stock-based compensation - Summary of incentive plan for members of management (Details) - Performance Based Shares - $ / shares
9 Months Ended 12 Months Ended
Sep. 30, 2023
Dec. 31, 2022
Restricted Stock    
Non-vested at beginning of period 281,963 321,883
Granted 251,658 194,791
Performance Shares Quantity Adjustment 16,374 6,947
Vested (232,717) (240,033)
Forfeited (16,082) (1,625)
Non-vested at end of period 301,196 281,963
Weighted-Average Grant Date Fair Value    
Non-vested at beginning of period $ 56.50 $ 47.98
Granted 66.79 84.29
Performance Shares Quantity Adjustment 76.07 78.02
Vested 66.38 66.11
Forfeited 55.56 78.86
Non-vested at end of period $ 58.14 $ 56.50