Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2011	Dec. 31, 2010
Class A [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	180,000,000	90,000,000
Common stock, shares issued	52,717,553	51,861,249
Common stock, shares outstanding	40,257,656	39,426,351
Treasury stock, shares	12,459,897	12,434,898
Class B [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	30,000,000	15,000,000
Common stock, shares issued	2,192,473	2,409,027
Common stock, shares outstanding	2,192,473	2,409,027