Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Income Taxes
Consolidated provision for income taxes	$ 15.5	$ 15.7	$ 28.4	$ 28.5	$ 34.3	$ 32.7
Consolidated effective federal and state income tax rates (as a percent)	37.70%	38.30%	38.20%	38.10%	38.50%	37.40%