CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Trade accounts receivable, allowance for doubtful accounts (in dollars)	$ 10.4	$ 9.7
Preferred Stock, par value (in dollars per share)	$ 0.10	$ 0.10
Preferred Stock, shares authorized	5,000,000	5,000,000
Preferred Stock, shares issued	0	0
Preferred Stock, shares outstanding	0	0
Class A Common Stock
Common Stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common Stock, shares authorized	80,000,000	80,000,000
Common Stock, votes per share (Number of votes)	1	1
Common Stock, issued shares	28,634,412	28,673,639
Common Stock, outstanding shares	28,634,412	28,673,639
Class B Common Stock
Common Stock, par value (in dollars per share)	$ 0.10	$ 0.10
Common Stock, shares authorized	25,000,000	25,000,000
Common Stock, votes per share (Number of votes)	10	10
Common Stock, issued shares	6,588,680	6,588,680
Common Stock, outstanding shares	6,588,680	6,588,680