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Share-Based Compensation Plans (Details) - shares
6 Months Ended 12 Months Ended
Jun. 30, 2018
Dec. 31, 2017
Restricted Stock Granted in Period 486,769 946,570
Class B Common Stock Bonus [Member]    
Restricted Stock Granted in Period   513,570
Restricted stock requisite service period 3 years  
Class B Common Stock Key Employees [Member]    
Restricted stock requisite service period 10 years 10 years