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 |