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Share-Based Compensation - Share-based compensation expense (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Share based compensation expense | $ 69,892 | $ 63,848 | $ 55,935
Share based compensation expense, net of tax | 60,345 | 55,502 | 49,179
Options and SARs |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Share based compensation expense | 11,744 | 12,866 | 16,272
Share based compensation expense, net of tax | 10,388 | 11,450 | 14,894
Restricted Common Shares And Restricted Units |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Share based compensation expense | 41,284 | 38,988 | 34,025
Share based compensation expense, net of tax | 34,599 | 32,999 | 29,044
Performance Awards |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Share based compensation expense | 14,729 | 8,949 | 4,414
Share based compensation expense, net of tax | 13,380 | 8,295 | 4,127
Employee Share Purchase Plan |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Share based compensation expense | 2,135 | 3,045 | 1,224
Share based compensation expense, net of tax | $ 1,978 | $ 2,758 | $ 1,114

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