v3.25.1
Business Segments (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Dec. 31, 2024
Segment Reporting Information [Line Items]      
Revenues $ 65,571 $ 53,289  
Cost of sales 55,917 46,271  
Earnings of unconsolidated operations 15,986 13,307  
Operating expenses 17,958 15,568  
Operating profit (loss) 7,682 4,757  
Expenditures for property, plant and equipment and acquisition of mineral interests 8,808 14,483  
Depreciation, depletion and amortization 6,793 5,692  
Total assets 634,187   $ 631,687
Operating segments | Coal Mining      
Segment Reporting Information [Line Items]      
Revenues 19,239 15,545  
Cost of sales 22,570 20,943  
Earnings of unconsolidated operations 14,463 12,007  
Operating expenses 7,341 7,026  
Operating profit (loss) 3,791 (417)  
Expenditures for property, plant and equipment and acquisition of mineral interests 617 1,794  
Depreciation, depletion and amortization 2,018 2,214  
Total assets 116,649   125,301
Operating segments | NAMining      
Segment Reporting Information [Line Items]      
Revenues 31,526 24,483  
Cost of sales 28,378 21,671  
Earnings of unconsolidated operations 969 1,365  
Operating expenses 2,147 1,822  
Operating profit (loss) 1,970 2,355  
Expenditures for property, plant and equipment and acquisition of mineral interests 6,754 5,818  
Depreciation, depletion and amortization 2,702 2,256  
Total assets 210,990   204,889
Operating segments | Minerals Management      
Segment Reporting Information [Line Items]      
Revenues 10,902 10,401  
Cost of sales 2,244 1,364  
Earnings of unconsolidated operations 554 (65)  
Operating expenses 1,305 1,042  
Operating profit (loss) 7,907 7,930  
Expenditures for property, plant and equipment and acquisition of mineral interests 807 136  
Depreciation, depletion and amortization 1,908 993  
Total assets 99,702   99,905
Unallocated Items      
Segment Reporting Information [Line Items]      
Revenues 4,400 3,262  
Cost of sales 3,237 2,712  
Operating expenses 7,165 5,678  
Operating profit (loss) (6,002) (5,128)  
Expenditures for property, plant and equipment and acquisition of mineral interests 630 6,735  
Depreciation, depletion and amortization 165 229  
Total assets 206,846   $ 201,592
Eliminations      
Segment Reporting Information [Line Items]      
Revenues (496) (402)  
Cost of sales (512) (419)  
Operating profit (loss) $ 16 $ 17