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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, 2018
Dec. 31, 2017
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 1,067,296  
Granted, Number of shares 333,959  
Vested, Number of shares (39,465)  
Forfeited or expired, Number of shares (72,566)  
Number of shares, Non-vested end of year 1,289,224 1,067,296
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 $ 16.34  
Weighted average fair value, Granted 25.96  
Weighted average fair value, Vested 19.54  
Weighted average fair value, Forfeited or expired 16.54  
Weighted average fair value, Non-vested end of year $ 18.72 $ 16.34
Remaining contractual life, Non-vested 1 year 9 months 24 days 2 years 2 months 24 days
Remaining contractual life, Granted 3 years