Accumulated Other Comprehensive Income (Loss) (Components of accumulated comprehensive loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	$ 236.0	$ 212.2	$ 191.9
Other comprehensive income (loss)	24.8	(12.7)	(16.0)
Ending balance	288.0	236.0	212.2
Cumulative Translation Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(30.8)	(16.9)	(5.1)
Other comprehensive income (loss)	19.2	(13.9)	(11.8)
Ending balance	(11.6)	(30.8)	(16.9)
Pension and Postretirement Benefits
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(11.9)	(13.1)	(8.9)
Other comprehensive income (loss)	5.6	1.2	(4.2)
Ending balance	(6.3)	(11.9)	(13.1)
Accumulated Other Comprehensive (Loss) Income
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(42.7)	(30.0)	(14.0)
Ending balance	$ (17.9)	$ (42.7)	$ (30.0)