Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2012	Dec. 31, 2011
Treasury stock, shares	1,306,177	1,201,051
Class A
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	80,000,000	80,000,000
Common stock, shares issued	66,958,867	56,778,718
Common stock, shares outstanding	65,652,690	55,577,667