Segment Information (Narrative) (Details)	6 Months Ended
	Jun. 30, 2022 segment Properties
Segment Reporting Information [Line Items]
Number of reportable segments | segment	2
United States Segment [Member] | Producing mine complexes, Buchanan and Logan [Member]
Segment Reporting Information [Line Items]
Portfolio of operating mines and development projects (number)	2
United States Segment [Member] | Idled mine complex (Greenbrier) [Member]
Segment Reporting Information [Line Items]
Portfolio of operating mines and development projects (number)	1
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