Business Segments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Revenues	$ 214,794	$ 241,719
Operating (loss) profit	(70,137)	69,986
Expenditures for property, plant and equipment and acquisition of mineral interests	82,122	54,447
Depreciation, depletion and amortization	29,387	26,816
Operating Segments | Coal Mining customer
Segment Reporting Information [Line Items]
Revenues	85,415	95,204
Operating (loss) profit	(71,342)	38,309
Expenditures for property, plant and equipment and acquisition of mineral interests	6,609	14,853
Depreciation, depletion and amortization	17,569	17,074
Operating Segments | NAMining customer
Segment Reporting Information [Line Items]
Revenues	90,532	85,664
Operating (loss) profit	3,348	2,202
Expenditures for property, plant and equipment and acquisition of mineral interests	36,073	13,203
Depreciation, depletion and amortization	8,172	6,457
Operating Segments | Minerals Management
Segment Reporting Information [Line Items]
Revenues	32,985	60,242
Operating (loss) profit	19,418	52,214
Expenditures for property, plant and equipment and acquisition of mineral interests	38,881	13,388
Depreciation, depletion and amortization	3,067	3,026
Unallocated Items
Segment Reporting Information [Line Items]
Revenues	8,459	2,952
Operating (loss) profit	(21,461)	(23,233)
Expenditures for property, plant and equipment and acquisition of mineral interests	559	13,003
Depreciation, depletion and amortization	579	259
Eliminations
Segment Reporting Information [Line Items]
Revenues	(2,597)	(2,343)
Operating (loss) profit	$ (100)	$ 494