Consolidated Statement of Changes in Equity (Parenthetical) - shares	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Class A Common Stock repurchased	3,599,107	44,114
Class A Common Shares [Member]
Stock Issued During Period, Shares, Share-based Compensation, Gross	209,357	296,580
Additional Paid-in Capital [Member] \| Class A Common Shares [Member]
Settlement of Deferred Stock Awards Shares	21,567	17,661
Conversion of Class B Common Stock to Class A Common Stock [Member] \| Common Stock [Member] \| Class A Common Shares [Member]
Stock Issued During Period, Shares, Conversion of Convertible Securities	160,000	45,000

Number of shares issued during the period as a result of the conversion of convertible securities.

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