CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 10,952	$ 4,782
Class A common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Class A common stock, shares authorized	199,300	199,300
Class A common stock, shares issued	99,301	98,181
Class A common stock, shares outstanding	84,395	92,433
Treasury stock, at cost, shares held	14,906	5,749