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Debt - Activity (Details) - USD ($) | Sep. 30, 2023 | Dec. 31, 2022 | Apr. 30, 2021
--- | --- | --- | ---
Debt Instrument [Line Items] |  |  |
Total debt | $ 512,000,000.0 | $ 527,700,000 |
Industrial revenue bonds, variable |  |  |
Debt Instrument [Line Items] |  |  |
Hancock County industrial revenue bonds ("IRBs") due April 1, 2028, interest payable quarterly | $ 7,800,000 | 7,800,000 |
Maximum variable interest rate | 12.00% |  |
Effective interest rate | 4.11% |  |
Revolving credit facility | U.S. revolving credit facility |  |  |
Debt Instrument [Line Items] |  |  |
Revolving credit facility | $ 68,200,000 | 90,000,000.0 |
Effective interest rate | 9.25% |  |
Revolving credit facility | Iceland revolving line of credit |  |  |
Debt Instrument [Line Items] |  |  |
Revolving credit facility | $ 0 | 35,000,000.0 |
Effective interest rate | 8.40% |  |
Casthouse Facility | Iceland revolving line of credit |  |  |
Debt Instrument [Line Items] |  |  |
Revolving credit facility | $ 3,100,000 | 0 |
Secured debt | 86,200,000 | 49,400,000 |
Financing fees | $ 700,000 |  |
Effective interest rate | 8.77% |  |
Iceland term facility | Iceland revolving line of credit |  |  |
Debt Instrument [Line Items] |  |  |
Revolving credit facility | $ 4,800,000 | 13,300,000 |
Secured debt | 0 | 1,200,000 |
Financing fees | $ 0 |  |
Stated interest rate, percentage | 3.20% |  |
Effective interest rate | 6.88% |  |
Vlissingen facility agreement | Iceland revolving line of credit |  |  |
Debt Instrument [Line Items] |  |  |
Revolving credit facility | $ 100,000 | 0 |
Secured debt | $ 10,000,000.0 | 0 |
Stated interest rate, percentage | 8.75% |  |
Senior secured notes, 7.5% | Senior notes |  |  |
Debt Instrument [Line Items] |  |  |
7.5% senior secured notes due April 1, 2028, net of financing fees of $2.8 million at September 30, 2023, interest payable semiannually | $ 247,200,000 | 246,600,000 |
Financing fees | $ 2,800,000 |  |
Stated interest rate, percentage | 7.50% |  | 7.50%
Senior convertible notes, 2.75% | Senior notes |  |  |
Debt Instrument [Line Items] |  |  |
2.75% convertible senior notes due May 1, 2028, net of financing fees of $1.6 million at September 30, 2023, interest payable semiannually | $ 84,600,000 | $ 84,400,000 |
Financing fees | $ 1,600,000 |  |
Stated interest rate, percentage | 2.75% |  |

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