Summary of Significant Accounting Policies, Narrative, Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment
Interest expense capitalized as construction in progress	$ 2.2	$ 2.9	$ 1.8
Depreciation expense	38.3	34.5	30.8
Non-cash impairment charges	19.2	2.8	0.1
Fabricated Products | Idled equipment
Property, Plant and Equipment
Non-cash impairment charges	$ 0.8	$ 0.2	$ 0.1
Minimum | Land improvements
Property, Plant and Equipment
Property, plant and equipment useful lives (in years)	3 years
Minimum | Buildings and leasehold improvements
Property, Plant and Equipment
Property, plant and equipment useful lives (in years)	15 years
Minimum | Machinery and equipment
Property, Plant and Equipment
Property, plant and equipment useful lives (in years)	1 year
Minimum | Capital lease assets
Property, Plant and Equipment
Property, plant and equipment useful lives (in years)	3 years
Maximum | Land improvements
Property, Plant and Equipment
Property, plant and equipment useful lives (in years)	25 years
Maximum | Buildings and leasehold improvements
Property, Plant and Equipment
Property, plant and equipment useful lives (in years)	45 years
Maximum | Machinery and equipment
Property, Plant and Equipment
Property, plant and equipment useful lives (in years)	24 years
Maximum | Capital lease assets
Property, Plant and Equipment
Property, plant and equipment useful lives (in years)	5 years