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Commitments and Contingencies (Details) | Apr. 09, 2021 USD ($) | Mar. 31, 2021 USD ($) | Aug. 31, 2018 USD ($) | Dec. 31, 2014 USD ($) | Dec. 31, 2000 assessment
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SWM-B Brazilian Mill | Raw Materials Assessment |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Liability recorded |  | $ 8,600,000 |  |  |
SWM-B Brazilian Mill | Raw Materials Assessment | Subsequent event |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Loss contingency accrual, payments | $ 2,600,000 |  |  |  |
Reduction of tax liability, percent | 70.00% |  |  |  |
Recognized total benefit on settlement | $ 6,100,000 |  |  |  |
SWM-B Brazilian Mill | Raw Materials Assessment | Subsequent event | Interest expense |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Recognized total benefit on settlement | 4,600,000 |  |  |  |
SWM-B Brazilian Mill | Raw Materials Assessment | Subsequent event | Other Expense |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Recognized total benefit on settlement | $ 1,600,000 |  |  |  |
Unfavorable Regulatory Action | Raw Materials Assessment |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Number of assessments from the tax authorities regarding ICMS taxes | assessment |  |  |  |  | 2
Unfavorable Regulatory Action | Electricity Assessment |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Number of assessments from the tax authorities regarding ICMS taxes | assessment |  |  |  |  | 4
Unfavorable Regulatory Action | Electricity Assessment One |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Electricity Assessment |  |  |  | $ 3,300,000 |
Unfavorable Regulatory Action | Second Electricity Assessment |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Electricity Assessment |  |  |  | $ 6,300,000 |
Unfavorable Regulatory Action | Electricity Assessment Three |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Electricity Assessment |  |  | $ 500,000 |  |
Unfavorable Regulatory Action | Electricity Assessment Four |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Electricity Assessment |  |  | $ 7,000,000.0 |  |
Unfavorable Regulatory Action | Raw Materials Assessment And Remaining Electricity Assessments |  |  |  |  |
Loss Contingencies [Line Items] |  |  |  |  |
Liability recorded |  | $ 0 |  |  |

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- Definition The number of assessments from the tax authorities of the State of Rio de Janeiro for unpaid Imposto sobre circulacao de Mercadorias e Servicos (or ICMS) taxes, a form of value-added tax in Brazil. + References No definition available. + Details
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