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Commitments and Contingencies - Narrative (Details) tonOfCoal in Thousands, $ in Thousands | 1 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | ---
Apr. 30, 2024 tonOfCoal | Mar. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Jan. 31, 2023 USD ($) | Feb. 10, 2022 USD ($) | Feb. 21, 2020 USD ($) | Feb. 20, 2020 USD ($)
Subsequent Event |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |
Arrangement, term | 3 years |  |  |  |  |  |
DTA Funding |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |
Minimum royalty obligations, remainder of fiscal year- 2024 |  | $ 40,000 |  |  |  |  |
Minimum royalty obligations, year one |  | 25,000 |  |  |  |  |
Minimum royalty obligations, year two |  | 25,000 |  |  |  |  |
Minimum royalty obligations, year three |  | 25,000 |  |  |  |  |
Minimum royalty obligations, year four |  | 25,000 |  |  |  |  |
Minimum royalty obligations, year five |  | 25,000 |  |  |  |  |
Minimum royalty obligations, after year five |  | 25,000 |  |  |  |  |
Minimum | Subsequent Event |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |
Number of tons of coal allowed to be loaded | tonOfCoal | 1,200 |  |  |  |  |  |
Maximum | Subsequent Event |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |
Number of tons of coal allowed to be loaded | tonOfCoal | 2,000 |  |  |  |  |  |
Black Lung |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |
Collateral for black lung obligations |  |  |  |  | $ 10,000 | $ 65,700 | $ 2,600
Black Lung | Minimum |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |
Collateral for black lung obligations |  |  |  | $ 80,000 |  |  |
Black Lung | Maximum |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |
Collateral for black lung obligations |  |  |  | $ 100,000 |  |  |
Surety Bond |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |
Outstanding surety bonds |  | 177,588 |  |  |  |  |
Reclamation-Related Obligations | Collateral Pledged |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |
Restricted cash, restricted investments, and deposits |  | 34,227 |  |  |  |  |
ABL Facility |  |  |  |  |  |  |
Long-term Purchase Commitment [Line Items] |  |  |  |  |  |  |
Letters of credit outstanding |  | $ 61,282 | $ 60,896 |  |  |  |

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