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Financial Instruments (Narrative) (Details)
R$ in Thousands, $ in Thousands, lb in Millions
12 Months Ended
Dec. 31, 2019
USD ($)
lb
Dec. 31, 2019
BRL (R$)
lb
Dec. 31, 2018
USD ($)
lb
Dec. 31, 2019
BRL (R$)
Derivative [Line Items]        
Net asset (liability) $ (2,188)   $ (2,720)  
Weight of aluminum that hedged future purchase of aluminum to meet fixed-price forward sales contract obligations, lbs | lb 19.6 19.6 22.5  
Amounts of unrealized after-tax gains on derivative instruments $ (900)      
Terphane Ltda [Member]        
Derivative [Line Items]        
Annual Net Costs Mismatch Translation Exposure - Real vs US Dollar | R$   R$ 137,000    
Notional amount 26,150     R$ 102,793
Aluminum Futures Contracts        
Derivative [Line Items]        
Notional amount 20,200   $ 25,400  
Accrued Expenses [Member] | Aluminum Futures Contracts        
Derivative [Line Items]        
Net asset (liability) (1,253)   $ (1,630)  
Cash Flow Hedging [Member] | Foreign Currency Forwwards And Options [Member]        
Derivative [Line Items]        
Foreign Currency Cash Flow Hedge Derivative at Fair Value, Net $ (800)