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Fair Value Disclosure (Narrative) (Details) - USD ($) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Gain on equity securities | $ 1,805 | $ 1,958 |
Business interruption insurance recoveries | 13,612 | 0 |
Long-term debt | 99,430 | 35,800 |
Fair Value, Nonrecurring | MLMC |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Non-cash asset impairment charge |  | 65,900 |
Fair Value, Nonrecurring | Coal Mining |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Non-cash asset impairment charge |  | 60,800 |
Fair Value, Nonrecurring | Mineral Management |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Non-cash asset impairment charge |  | 5,100 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Gain on equity securities | 300 | 400 |
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Reported Value Measurement |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Equity securities cost |  |  | $ 2,000
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fair Value, Measurements, Recurring | Bellaire |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Gain on equity securities | 1,500 | 1,600 |
Significant Other Observable Inputs (Level 2) |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Long-term debt fair value | $ 97,900 | $ 35,300 |

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