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Debt - Casthouse Facility Narrative (Details) € in Millions | Nov. 02, 2021 USD ($) | Mar. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Dec. 09, 2022 USD ($) | Sep. 30, 2022 EUR (€)
--- | --- | --- | --- | --- | ---
Casthouse Facility |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Debt instrument, term | 8 years |  |  |  |
Credit facility maximum amount | $ 130,000,000 |  |  |  |
Debt instrument, quarterly installment fee | 1.739% |  |  |  |
Debt instrument, remaining payment after drawdown of funds | 60.00% |  |  |  |
Medium-term notes, outstanding borrowings |  | $ 130,000,000 |  |  |
Casthouse Facility | Iceland revolving line of credit |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate, percentage |  | 8.84% |  |  |
Secured debt |  | $ 119,800,000 | $ 98,800,000 |  |
Medium-term Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Credit facility maximum amount | € |  |  |  |  | € 13.6
Iceland Term Facility | Iceland revolving line of credit |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate, percentage |  | 3.20% |  |  |
Vlissingen facility agreement | Iceland revolving line of credit |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate, percentage |  | 8.75% |  |  |
Face amount |  |  |  | $ 90,000,000 |
Secured debt |  | $ 10,000,000 |  |  |
Industrial revenue bonds, variable |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maximum variable interest rate |  | 12.00% |  |  |
Surety Bond |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Loss contingency accrual |  | $ 6,600,000 |  |  |

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