CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 3,332,000	$ 3,008,000
Total assets of variable interest entities	44,900,000	33,500,000
Total liabilities of variable interest entities	$ 11,200,000	$ 14,400,000
Class A Common Stock
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized	500,000,000	500,000,000
Common Stock, shares issued	52,280,511	52,022,086
Common Stock, shares outstanding	52,280,511	52,022,086
Class B Common Stock
Common Stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common Stock, shares authorized	140,000,000	140,000,000
Common Stock, shares issued	28,933,859	28,933,859
Common Stock, shares outstanding	28,933,859	28,933,859