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Derivative Financial Instruments (Narrative) (Details) R$ in Thousands, $ in Thousands, lbs in Millions | 9 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | ---
Sep. 30, 2020 BRL (R$) | Sep. 30, 2021 USD ($) | Sep. 30, 2020 USD ($) lbs | Sep. 30, 2020 BRL (R$) lbs | Dec. 31, 2019 USD ($) lbs
Derivative [Line Items] |  |  |  |  |
Amounts of unrealized after tax gains (losses) to be Reclassified within Twelve Months |  | $ 100 |  |  |
Aluminum Futures Contracts |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Notional Amount |  |  | $ 15,700 |  | $ 20,200
Net asset (liability), Fair Value |  |  | $ (124) |  | $ (1,253)
Commitment Under Cash Flow Hedges, Mass | lbs |  |  | 16.8 | 16.8 | 19.6
Terphane Ltda [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative, Notional Amount |  |  | $ 18,450 | R$ 91,056 |
Accrued Expenses [Member] | Derivatives Designated As Hedging Instruments [Member] | Aluminum Futures Contracts |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Derivative Asset, Fair Value, Gross Asset |  |  | 659 |  | $ 6
Derivative Liability, Fair Value, Gross Liability |  |  | 783 |  | $ 1,259
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 |  |  | $ 2,400 |  |
Oct-2018 [Member] | Terphane Ltda [Member] |  |  |  |  |
Derivative [Line Items] |  |  |  |  |
Annual Net Costs Mismatch Translation Exposure - Real vs US Dollar | R$ | R$ 134,000 |  |  |  |

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