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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) |  |  |

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