Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Class A
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	12,000,000	12,000,000
Common Stock, shares issued	6,577,100	6,595,308
Common Stock, shares outstanding	6,577,100	6,595,308
Class B
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	150,000,000	150,000,000
Common Stock, shares issued	84,092,304	86,947,407
Common Stock, shares outstanding	84,092,304	86,947,407
Class C
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	1,200,000	1,200,000
Common Stock, shares issued	661,688	663,940
Common Stock, shares outstanding	661,688	663,940
Class D
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	5,000,000	5,000,000
Common Stock, shares issued	18,653	20,868
Common Stock, shares outstanding	18,653	20,868