Supplemental Data - Property, Plant, and Equipment, Accrued Expense, Noncurrent Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment - Net
Gross property, plant and equipment	$ 850.5	$ 755.6
Less accumulated depreciation	425.3	391.0
Net Property, Plant and Equipment	425.2	364.6
Depreciation expense	28.3	27.1	$ 24.8
Interest expense capitalized	0.0	0.8	$ 0.2
Accrued Expenses
Accrued salaries and employee benefits	29.6	26.3
Amounts due to customers	7.2	7.3
Accrued interest	1.3	1.3
Accrued income taxes	4.2	2.0
Other	15.2	14.3
Total	57.5	51.2
Noncurrent Employee Benefits
Pension benefits	59.8	49.0
Post-employment benefits other than pensions	40.5	37.7
Total	100.3	86.7
Long-term disability benefits due to Terrace Bay retirees	1.8	1.3
Land and land improvements
Property, Plant and Equipment - Net
Gross property, plant and equipment	20.2	18.3
Buildings
Property, Plant and Equipment - Net
Gross property, plant and equipment	157.7	126.1
Machinery and equipment
Property, Plant and Equipment - Net
Gross property, plant and equipment	650.8	597.5
Construction in progress
Property, Plant and Equipment - Net
Gross property, plant and equipment	$ 21.8	$ 13.7