Derivative Financial Instruments (Narrative) (Details) $ in Thousands, lb in Millions	9 Months Ended	12 Months Ended
Sep. 30, 2018 USD ($) lb	Dec. 31, 2017 USD ($) lb
Derivative [Line Items]
Amounts of unrealized after tax gains (losses) to be Reclassified within Twelve Months	$ 700
Aluminum Futures Contracts
Derivative [Line Items]
Notional Amount	$ 18,200	$ 8,200
Weight of aluminum that hedged future purchase of aluminum to meet fixed - price forward sales contract obligations, lbs \| lb	16.4	8.0
Net asset (liability), Fair Value	$ (793)	$ 562
Accrued Expenses [Member] \| Derivatives Designated As Hedging Instruments [Member] \| Aluminum Futures Contracts
Derivative [Line Items]
Derivative Asset, Fair Value, Gross Asset	201	578
Derivative Liability, Fair Value, Gross Liability	994	$ 16
Cash Flow Hedging [Member] \| Foreign Currency Forwwards And Options [Member]
Derivative [Line Items]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, before Tax	$ 2,300

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

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Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

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Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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Fair value of the assets less the liabilities of a derivative or group of derivatives.

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Nominal mass used to calculate payments on a derivative instrument.

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Fair value as of the balance sheet date of all foreign currency derivatives designated as cash flow hedging instruments.

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