Consolidated Statement of Changes in Equity (Parenthetical) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Class A Common Stock repurchased	111,289	832,232
Class A Common Shares [Member]
Stock Issued During Period, Shares, Share-based Compensation, Gross	164,732	115,897
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	100,000	0