CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Mar. 31, 2015	Dec. 31, 2014
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 4,387,000	$ 4,246,000
Total assets of variable interest entities (in dollars)	159,100,000	163,300,000
Total liabilities of variable interest entities (in dollars)	$ 31,600,000	$ 30,000,000
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	69,491,915	69,578,899
Common Stock, shares outstanding	69,491,915	69,578,899
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	25,928,357	25,928,357
Common Stock, shares outstanding	25,928,357	25,928,357