Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Accounts receivable, trade, allowance for doubtful accounts	$ 1,378	$ 3,092
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	45,000,000	45,000,000
Preferred stock, shares issued	0	0
Treasury stock, shares	656,013	194,060
Class A [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	360,000,000	360,000,000
Common Stock, Shares, Issued	61,247,043	58,628,764
Common Stock, Shares, Outstanding	60,591,030	58,434,704
Class B [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	90,000,000	90,000,000
Common Stock, Shares, Issued	11,784,408	13,534,408
Common Stock, Shares, Outstanding	11,784,408	13,534,408