XML 176 R159.htm IDEA: XBRL DOCUMENT v3.21.1
Stock-based compensation - Summary of incentive plan for members of management (Details) - Performance Based Shares - $ / shares
3 Months Ended 12 Months Ended
Mar. 31, 2021
Dec. 31, 2020
Restricted Stock    
Non-vested at beginning of period 358,512 345,365
Granted 124,613 253,943
Performance Shares Quantity Adjustment 46,704 (7)
Vested (193,946) (234,421)
Forfeited   (6,368)
Non-vested at end of period 335,883 358,512
Weighted-Average Grant Date Fair Value    
Non-vested at beginning of period $ 41.23 $ 41.68
Granted 66.84 42.49
Performance Shares Quantity Adjustment 51.48 48.79
Vested 57.16 42.64
Forfeited   44.26
Non-vested at end of period $ 42.96 $ 41.23