Consolidated Balance Sheets (Parenthetical) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Allowance for doubtful accounts	$ 4,131	$ 2,765
Preferred stock, par/stated value	$ 0.01	$ 0.01
Treasury stock, shares	24,162,676	23,697,671
Series A cumulative redeemable preferred stock
Preferred stock, par/stated value	$ 1,000.00	$ 1,000.00
Preferred stock, shares authorized	100,000,000	100,000,000
Preferred stock, shares issued	75,767	125,000
Preferred stock, shares outstanding	75,767	125,000
Class A Common Stock
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	750,000,000	750,000,000
Common stock, shares issued	182,682,073	160,783,484
Common stock, shares outstanding	158,519,394	137,085,813
Class B Common Stock
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	600,000,000	600,000,000
Common stock, shares issued	15,424,944	12,439,667
Common stock, shares outstanding	15,424,944	12,439,667
Class C Common Stock
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	644,871	644,871
Common stock, shares issued	644,871	644,871
Common stock, shares outstanding	644,871	644,871