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Earnings Per Common Share And Share Awards Summary Of Share-Based Award Transactions (Details) - SARs - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, SARS, Outstanding [Roll Forward]        
Number Of Shares, Outstanding Beginning Balance 36 30 30  
Number Of Shares, SARs granted 0 7 14  
Number Of Shares, SARS exercised (3)   (8)  
Number Of Shares, Outstanding Ending Balance 33   36 30
Number Of Shares, Exercisable as of March 31, 2021 26      
Number Of Shares, Unvested as of March 31, 2021 7      
Share-based Compensation Arrangement by Share-based Payment Award, SARs, Outstanding, Weighted Average Exercise Price [Roll Forward]        
Weighted Average Exercise Price, Outstanding Beginning Balance $ 139.16 $ 124.13 $ 124.13  
Weighted Average Exercise Price, SARs granted 0   137.40  
Weighted Average Exercise Price, SARS exercised 68.70   75.75  
Weighted Average Exercise Price, Outstanding Ending Balance 145.47   $ 139.16 $ 124.13
Weighted Average Exercise Price, Exercisable as of March 31, 2021 146.55      
Weighted Average Exercise Price, Unvested as of March 31, 2021 $ 141.37      
Average Remaining Contractual Term, Outstanding Beginning Balance 4 years 5 months 26 days   4 years 4 months 17 days 3 years 6 months 10 days
Average Remaining Contractual Term, Outstanding Ending Balance 4 years 5 months 26 days   4 years 4 months 17 days 3 years 6 months 10 days
Average Remaining Contractual Term, Exercisable as of March 31, 2021 4 years 10 days      
Average Remaining Contractual Term, Unvested as of March 31, 2021 6 years 2 months 26 days      
Aggregate Intrinsic Value, Outstanding Beginning Balance $ 903 $ 1,352 $ 1,352  
Aggregate Intrinsic Value, Outstanding Ending Balance 910   $ 903 $ 1,352
Aggregate Intrinsic Value, Exercisable as of March 31, 2021 738      
Aggregate Intrinsic Value, Unvested as of March 31, 2021 $ 172