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Debt - Activity (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Oct. 01, 2024 | Dec. 31, 2023 | Apr. 14, 2021 | Apr. 09, 2021
--- | --- | --- | --- | --- | ---
Debt Instrument [Line Items] |  |  |  |  |
Total | $ 528.2 |  | $ 479.2 |  |
Industrial Revenue Bonds, Variable |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Maximum variable interest rate | 12.00% |  |  |  |
Hancock County industrial revenue bonds ("IRBs") due April 2028, interest payable quarterly (variable interest rates (not to exceed 12%)) | $ 7.8 |  | 7.8 |  |
Revolving Credit Facility | U.S revolving credit facility |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Revolving credit facility | $ 20.0 |  | 23.7 |  |
Stated interest rate, percentage | 8.00% |  |  |  |
Revolving Credit Facility | Foreign line of credit |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Revolving credit facility | $ 34.0 |  | 0.0 |  |
Stated interest rate, percentage | 7.84% |  |  |  |
Casthouse Facility | Foreign line of credit |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Revolving credit facility | $ 9.0 |  | 5.5 |  |
Financing fees | 0.0 |  |  |  |
Secured debt | $ 114.2 |  | 98.8 |  |
Stated interest rate, percentage | 8.06% |  |  |  |
Iceland Term Facility | Foreign line of credit |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Revolving credit facility | $ 0.0 |  | 1.3 |  |
Stated interest rate, percentage | 3.20% |  |  |  |
Vlissingen Facility Agreement | Foreign line of credit |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Revolving credit facility | $ 0.0 |  | 10.0 |  |
Secured debt | $ 10.0 |  | 0.0 |  |
Stated interest rate, percentage | 7.99% | 8.75% |  |  |
Senior Secured Notes, 7.5% | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Financing fees | $ 1.9 |  |  |  |
Stated interest rate, percentage | 7.50% |  |  | 7.50% |
7.5% senior secured notes due April 1, 2028, net of financing fees of $1.9 million at December 31, 2024, interest payable semiannually | $ 248.1 |  | 247.4 |  |
Senior Convertible Notes, 2.75% | Senior Notes |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Financing fees | $ 1.2 |  |  |  |
Stated interest rate, percentage | 2.75% |  |  |  | 2.75%
2.75% convertible senior notes due May 1, 2028, net of financing fees of $1.2 million at December 31, 2024, interest payable semiannually | $ 85.1 |  | $ 84.7 |  |
Industrial revenue bonds due 2028 |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |
Stated interest rate, percentage | 3.75% |  |  |  |

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