Commitments and Contingencies, Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accrual for Environmental Loss Contingencies, Gross, Fiscal Year Maturity
Rental expense	$ 7.9	$ 8.5	$ 8.2
Environmental accrual	$ 16.6	$ 17.2	$ 18.6	$ 19.3
Expected period related to remediation expenditures for environmental contingencies	30 years
Estimated environmental contingency loss exposure in excess of current accrual	$ 12.5
Time period within which Company's recorded estimate of its obligation may change	12 months
Minimum
Accrual for Environmental Loss Contingencies, Gross, Fiscal Year Maturity
Period for feasibility study completion	18 months
Maximum
Accrual for Environmental Loss Contingencies, Gross, Fiscal Year Maturity
Period for feasibility study completion	24 months