Business Segments (Segment Reporting Information) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Segment Reporting Information [Line Items]
Revenues	$ 277,198	$ 237,708
Cost of sales	238,725	207,952
Earnings of unconsolidated operations	61,823	57,476
Operating expenses	78,315	65,139
Operating profit (loss)	21,981	35,705
Expenditures for property, plant and equipment and acquisition of mineral interests	53,286	55,419
Depreciation, depletion and amortization	25,277	24,652
Total assets	661,228	631,687
Operating Segments | Utility Coal Mining
Segment Reporting Information [Line Items]
Revenues	88,188	68,611
Cost of sales	94,155	79,375
Earnings of unconsolidated operations	54,471	51,821
Operating expenses	31,349	30,358
Operating profit (loss)	17,155	24,311
Expenditures for property, plant and equipment and acquisition of mineral interests	8,020	8,292
Depreciation, depletion and amortization	8,815	9,476
Total assets	125,715	125,301
Operating Segments | Contract Mining
Segment Reporting Information [Line Items]
Revenues	140,013	119,600
Cost of sales	129,876	110,821
Earnings of unconsolidated operations	4,789	5,010
Operating expenses	9,159	8,017
Operating profit (loss)	5,767	5,772
Expenditures for property, plant and equipment and acquisition of mineral interests	31,968	30,556
Depreciation, depletion and amortization	10,854	9,811
Total assets	213,571	204,889
Operating Segments | Minerals and Royalties
Segment Reporting Information [Line Items]
Revenues	37,630	34,579
Cost of sales	5,666	5,234
Earnings of unconsolidated operations	2,571	647
Operating expenses	5,427	1,065
Operating profit (loss)	29,108	28,927
Expenditures for property, plant and equipment and acquisition of mineral interests	7,710	1,079
Depreciation, depletion and amortization	4,579	4,273
Total assets	115,545	99,905
Unallocated Items
Segment Reporting Information [Line Items]
Revenues	15,080	17,707
Cost of sales	12,654	15,323
Earnings of unconsolidated operations	(8)	(2)
Operating expenses	32,380	25,699
Operating profit (loss)	(29,962)	(23,317)
Expenditures for property, plant and equipment and acquisition of mineral interests	5,588	15,492
Depreciation, depletion and amortization	1,029	1,092
Total assets	206,397	201,592
Eliminations
Segment Reporting Information [Line Items]
Revenues	(3,713)	(2,789)
Cost of sales	(3,626)	(2,801)
Operating profit (loss)	$ (87)	$ 12