Derivative Financial Instruments and Related Hedging Programs, Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2020	Dec. 31, 2018
Derivative [Line Items]
Margin deposits with counterparties	$ 0
Customer Deposits, Current	0
Derivative Asset	25,300,000	$ 5,800,000
Derivative Instruments in Hedges, at Fair Value, Net	$ 24,500,000	4,000,000
Debt Instrument, Term	8 months
Alloy Metal Hedge | Designated as Hedging Instrument
Derivative [Line Items]
Gain (Loss) on Cash Flow Hedge Ineffectiveness, Net	$ 0
Maximum | Alloy Metal Hedge | Designated as Hedging Instrument | Purchase
Derivative [Line Items]
Derivative, Remaining Maturity	6 months
Scenario, Forecast | Natural Gas Member
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage				55.00%	70.00%
Scenario, Forecast | Electricity Member
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount, Percent of Required Need, Coverage				46.00%	55.00%
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent
Derivative [Line Items]
OCI, before Reclassifications, before Tax, Attributable to Parent	$ 2,000,000	$ (200,000)	$ (500,000)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent | Alloy Metal Hedge
Derivative [Line Items]
OCI, before Reclassifications, before Tax, Attributable to Parent	$ (500,000)