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Derivative Financial Instruments (Narrative) (Details)
$ in Thousands, lb in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2016
USD ($)
lb
Dec. 31, 2015
USD ($)
lb
Derivative [Line Items]    
Amounts of unrealized after tax gains (losses) to be Reclassified within Twelve Months $ 100  
Aluminum Futures Contracts    
Derivative [Line Items]    
Notional Amount $ 10,500 $ 16,600
Weight of aluminum that hedged future purchase of aluminum to meet fixed - price forward sales contract obligations, lbs | lb 12.9 18.9
Net asset (liability), Fair Value $ (177) $ (1,753)
Accrued Expenses [Member] | Derivatives Not Designated As Hedging Instruments | Aluminum Futures Contracts    
Derivative [Line Items]    
Derivative Liability, Fair Value, Gross Liability 0 0
Accrued Expenses [Member] | Derivatives Designated As Hedging Instruments [Member] | Aluminum Futures Contracts    
Derivative [Line Items]    
Derivative Asset, Fair Value, Gross Asset 59 44
Derivative Liability, Fair Value, Gross Liability $ 236 $ 1,797