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Financial Instruments (Summary Of Location And Fair Value Of Derivative Financial Instruments) (Details) - USD ($)
$ in Thousands
Dec. 31, 2017
Dec. 31, 2016
Derivatives, Fair Value [Line Items]    
Net asset (liability) $ (558) $ 0
Aluminum Futures Contracts | Designated as Hedging Instrument | Prepaid Expenses and Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Asset derivatives 578  
Aluminum futures contracts (16)  
Aluminum Futures Contracts | Designated as Hedging Instrument | Accrued Expenses    
Derivatives, Fair Value [Line Items]    
Asset derivatives   308
Aluminum futures contracts   (37)
Aluminum Futures Contracts | Not Designated as Hedging Instrument [Member] | Prepaid Expenses and Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Aluminum futures contracts $ 0  
Aluminum Futures Contracts | Not Designated as Hedging Instrument [Member] | Accrued Expenses    
Derivatives, Fair Value [Line Items]    
Asset derivatives   0
Aluminum futures contracts   $ 0