Consolidated Balance Sheets (Parenthetical) (USD $)	Jun. 30, 2013	Dec. 31, 2012
Common Class A [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	350,000,000	350,000,000
Common stock, shares issued	102,855,343	102,687,323
Class A Treasury common stock, shares	27,029,526	25,661,817
Common Class B [Member]
Common stock, par value	$ 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