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Commitments and Contingencies - Narrative (Details) - USD ($) $ in Thousands |  | 3 Months Ended | 6 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Jan. 14, 2025 | Jun. 30, 2026 | Jun. 30, 2025 | Jun. 30, 2026 | Jun. 30, 2025 | Apr. 30, 2026 | Dec. 31, 2025 | Jan. 31, 2025
Black Lung |  |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |  |
Required documents submission period | 60 days |  |  |  |  |  |  |
Surety Bond |  |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |  |
Outstanding surety bonds |  | $ 171,479 |  | $ 171,479 |  |  |  |
Reclamation-Related Obligations | Collateral Pledged |  |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |  |
Restricted cash, restricted investments, and deposits |  | 28,562 |  | 28,562 |  |  |  |
ABL Facility |  |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |  |
Letters of credit outstanding |  | 40,710 |  | $ 40,710 |  |  | $ 41,254 |
Minimum | Black Lung |  |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |  |
Collateral for black lung obligations |  |  |  |  |  |  |  | $ 80,000
Maximum | Black Lung |  |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |  |
Collateral for black lung obligations |  |  |  |  |  |  |  | $ 100,000
Additional DTA Investment |  |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |  |
Arrangement, term |  |  |  | 5 years |  |  |  |
Partnership Interest in Centauri Ground Support LLC |  |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |  |
Other commitment |  |  |  |  |  | $ 9,408 |  |
Other commitment (as a percent) |  |  |  |  |  | 49.00% |  |
Coal |  |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |  |
Coal royalty expense |  | $ 26,611 | $ 26,402 | $ 53,850 | $ 50,487 |  |  |

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