Consolidated Statement of Changes in Equity (Parenthetical) - shares	3 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Class A Common Stock repurchased	31,256	107	111,289	893,705	1,873,170	832,232
Class A Common Shares [Member]
Stock Issued During Period, Shares, Share-based Compensation, Gross	112,347	38,512	164,732	72,925	42,102	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	0	40,746	100,000	130,000	30,000	0