Post-retirement Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	$ 0.2
Pension expense	0.1	$ 0.1	$ 0.1
Accrued liability	2.7	2.7
Projected benefit obligations under this plan	2.7
Defined Contribution Plan, Employer Discretionary Contribution Amount	17.6	$ 17.5	$ 17.2
Postretirement Health Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	1.9
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	1.6
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	1.6
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	1.7
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	1.7
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	8.2
Business Combination Acquiree [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Accumulated Benefit Obligation	$ 52.8