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Property, Plant, Equipment and Mine Development | 9 Months Ended
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Sep. 30, 2025
Property, Plant and Equipment [Abstract] |
Property, Plant, Equipment and Mine Development | Property, Plant, Equipment and Mine Development The composition of property, plant, equipment and mine development, net, as of September 30, 2025 and December 31, 2024 is set forth in the table below:
| September 30, 2025 |  | December 31, 2024
| (Dollars in millions)
Land and coal interests | $ | 2,645.1 |  |  | $ | 2,648.5 |
Buildings and improvements | 754.1 |  |  | 726.7 |
Machinery and equipment | 2,295.7 |  |  | 2,078.8 |
Less: Accumulated depreciation, depletion and amortization | (2,619.4) |  |  | (2,372.5) |
Property, plant, equipment and mine development, net | $ | 3,075.5 |  |  | $ | 3,081.5 |
At-Risk Assets The Company identified certain assets with an aggregate carrying value of approximately $68 million at September 30, 2025 in its Other U.S. Thermal segment whose recoverability is most sensitive to customer concentration risk.

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- Definition The entire disclosure for long-lived, physical asset used in normal conduct of business and not intended for resale. Includes, but is not limited to, work of art, historical treasure, and similar asset classified as collections. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 360 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/360/tableOfContent Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 6 -SubTopic 360 -Topic 958 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477798/958-360-50-6 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (d) -SubTopic 360 -Topic 958 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477798/958-360-50-1 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 7 -SubTopic 360 -Topic 958 -Publisher FASB -URI https://asc.fasb.org/1943274/2147477798/958-360-50-7 + Details
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