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Share-Based Compensation And Share Repurchase Plans (Summary Of Vested And Unvested Stock Options) (Details) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average remaining years of contractual life, Vested 1 year 7 months 20 days 1 year 10 months 13 days 2 years 3 months 10 days
Aggregate intrinsic value, Vested   $ 136,350 $ 1,306,643
Weighted average remaining years of contractual life, Nonvested 2 years 5 months 19 days 3 years 4 months 9 days 3 years 3 months 7 days
Aggregate intrinsic value, Nonvested $ 13,969   $ 223,885
Class A [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vested 418,435 273,866 231,124
Weighted average exercise price, Vested $ 13.87 $ 12.59 $ 12.38
Unvested 295,044 437,511 355,345
Weighted average exercise price, Nonvested $ 15.77 $ 15.78 $ 15.07