Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Accounts receivable, trade, allowance for doubtful accounts	$ 931	$ 1,378
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	898,447	656,013
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	61,692,561	61,247,043
Common Stock, Shares, Outstanding	60,794,114	60,591,030
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	11,484,408	11,784,408
Common Stock, Shares, Outstanding	11,484,408	11,784,408