CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Thousands, except Share data	Jun. 30, 2011	Dec. 31, 2010
Accounts receivable, allowance for doubtful accounts (in dollars)	$ 3,017	$ 3,216
Class A
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	51,998,503	50,284,052
Common Stock, shares outstanding	51,998,503	50,284,052
Class B
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	30,083,819
Common Stock, shares outstanding	28,933,859	30,083,819