Income Taxes (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Income Taxes
Effective income tax rate (as a percent)	32.70%	33.50%
Unrecognized income tax benefits	$ 4.3		$ 4.1
Gross unrecognized tax benefits that would impact effective tax rate	3.2		3.0
Unrecognized tax benefits that will be realized in the next twelve months as a result of the expiration of statute limitations	$ 0.3