CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Per Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 7,287	$ 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	98,576	98,181
Class A common stock, shares outstanding	92,602	92,433
Treasury stock, at cost, shares held	5,974	5,749