Income Taxes (Income Taxes) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current expense (benefit):
Federal	$ 14.3	$ (0.8)	$ 11.7
State	0.7	0.2	0.7
Foreign	7.6	6.6	6.0
Total	22.6	6.0	18.4
Deferred expense (benefit):
Federal	(5.4)	1.6	2.7
State	0.3	0.5	0.6
Foreign	0.7	0.7	(0.4)
Total	(4.4)	2.8	2.9
Income tax expense	$ 18.2	$ 8.8	$ 21.3