Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Allowance for doubtful accounts on trade receivables	$ 3.9	$ 3.2
Class A Common Stock
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	900,000,000	900,000,000
Common Stock, shares issued	49,986,651	49,986,651
Treasury Stock, at cost, shares	750,900	671,271
Class B Common Stock
Common Stock, par value	$ 0.01	$ 0.01
Common Stock, shares authorized	200,000,000	200,000,000
Common Stock, shares issued	3,125,000	3,125,000
Common Stock, shares outstanding	3,125,000	3,125,000