Segment Information (Narrative) (Details)	6 Months Ended
Jun. 30, 2025 Item segment
Segment Reporting Information [Line Items]
Number of reportable segments \| segment	2
Australia Segment [Member] \| Curragh producing mine complex [Member]
Segment Reporting Information [Line Items]
Minority Interest Ownership Percentage By Parent	100.00%
United States Segment [Member] \| Producing mine complexes [Member]
Segment Reporting Information [Line Items]
Portfolio of operating mines and development projects (number)	2
Minority Interest Ownership Percentage By Parent	100.00%
United States Segment [Member] \| Development properties, Mon Valley and Russell County [Member]
Segment Reporting Information [Line Items]
Portfolio of operating mines and development projects (number)	2

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 47
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-47

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 54
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-54

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-18

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration