Related Party Transactions (Details)	Dec. 31, 2017
Class B common stock \| Executive Chairman and Chairman of the Board and Director \| Terence E. Adderley
Related Party Transaction [Line Items]
Ownership percentage of parent company	93.00%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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