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Employee Compensation Plans - Summarizes of Company's Non-Vested ESP/EIP Awards (Details) - Common Class A [Member] - Restricted Stock - $ / shares
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]    
Number of shares, Non-vested beginning of year 1,534,278  
Granted, Number of shares 471,700  
Vested, Number of shares (623,981)  
Forfeited or expired, Number of shares (53,120)  
Number of shares, Non-vested end of year 1,328,877 1,534,278
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures    
Weighted average fair value, Non-vested beginning of year $ 20.34  
Weighted average fair value, Granted 23.84  
Weighted average fair value, Vested 17.91  
Weighted average fair value, Forfeited or expired 22.89  
Weighted average fair value, Non-vested end of year $ 22.63 $ 20.34
Remaining contractual life, Non-vested 1 year 10 months 24 days 1 year 4 months 24 days
Remaining contractual life, Granted 3 years