Derivative Instruments and Hedging Activities (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($) MMBTU t lb MW	Mar. 31, 2018 CAD ($) MMBTU t lb MW	Mar. 31, 2018 EUR (€) MMBTU t lb MW	Dec. 31, 2017 CAD ($) MMBTU t lb MW	Dec. 31, 2017 EUR (€) MMBTU t lb MW
Derivative [Line Items]
Derivative, Collateral, Right to Reclaim Cash	$ 0.0
Euro Member Countries, Euro
Derivative [Line Items]
Beginning Settlement Date	Apr. 01, 2018
Ending Settlement Date	Dec. 31, 2018
Canada, Dollars
Derivative [Line Items]
Beginning Settlement Date	Apr. 01, 2018
Ending Settlement Date	Dec. 31, 2021
Gains (losses) expected to be reclassified into cost of products sold within the next twelve months	$ (6.8)
Natural Gas [Member]
Derivative [Line Items]
Beginning Settlement Date	Apr. 01, 2018
Ending Settlement Date	Mar. 31, 2020
Gains (losses) expected to be reclassified into cost of products sold within the next twelve months	$ (0.5)
Zinc [Member]
Derivative [Line Items]
Beginning Settlement Date	Apr. 01, 2018
Ending Settlement Date	Dec. 31, 2019
Gains (losses) expected to be reclassified into cost of products sold within the next twelve months	$ (6.8)
Iron Ore [Member]
Derivative [Line Items]
Beginning Settlement Date	Apr. 01, 2018
Ending Settlement Date	Dec. 31, 2019
Electricity [Member]
Derivative [Line Items]
Beginning Settlement Date	Apr. 01, 2018
Ending Settlement Date	Dec. 31, 2019
Gains (losses) expected to be reclassified into cost of products sold within the next twelve months	$ 0.5
Commodity Contract [Member] | Nickel [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives | lb	0	0	0	500,000	500,000
Commodity Contract [Member] | Natural Gas [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives | MMBTU	37,843,000	37,843,000	37,843,000	41,338,000	41,338,000
Commodity Contract [Member] | Zinc [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives | lb	51,300,000	51,300,000	51,300,000	50,350,000	50,350,000
Commodity Contract [Member] | Iron Ore [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives | t	2,065,000	2,065,000	2,065,000	2,340,000	2,340,000
Commodity Contract [Member] | Electricity [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Derivatives | MW	1,308,000	1,308,000	1,308,000	1,553,000	1,553,000
Foreign Exchange Contract [Member] | Euro Member Countries, Euro
Derivative [Line Items]
Derivative, Notional Amount | €			€ 18,000,000.0		€ 26,000,000.0
Foreign Exchange Contract [Member] | Canada, Dollars
Derivative [Line Items]
Derivative, Notional Amount		$ 147,900,000		$ 148,100,000