CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Accounts receivable, allowance for doubtful accounts	$ 4,500	$ 4,246
Total assets of variable interest entities	155,300	163,300
Total liabilities of variable interest entities	$ 28,800	$ 30,000
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	69,535,162	69,578,899
Common Stock, shares outstanding	69,535,162	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