Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Income Taxes
Effective tax rate (as a percent)	32.00%	35.40%	32.70%	35.50%
Amount of unrecognized tax benefits	$ 17.4		$ 17.4		$ 16.5
Increase in unrecognized tax benefits			0.9
Gross accrued interest and penalties on unrecognized tax benefits	1.6		1.6		1.8
Unrecognized income tax benefits that, if recognized, would affect the effective tax rates	17.7		17.7		17.0
Unrecognized income tax benefits that, if recognized, would affect the effective tax rates , interest and penalties	1.0		1.0		$ 1.2
Significant changes to uncertain tax positions during the next twelve months	$ 0.0		$ 0.0