Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Jun. 30, 2016	Dec. 31, 2015
Common Class A [Member]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	350,000,000	350,000,000
Common stock, shares issued	107,439,137	106,907,772
Class A Treasury common stock, shares	28,580,112	28,401,898
Common Class B [Member]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	7,838,731	7,838,731
Common stock, shares outstanding	7,838,731	7,838,731