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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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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 460
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482425/460-10-50-4

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+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 954
-SubTopic 210
-Name Accounting Standards Codification
-Section 45
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480632/954-210-45-4

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 954
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