v3.26.1
Business Segments (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Segment Reporting [Line Items]          
Revenues $ 72,310 $ 68,235 $ 135,085 $ 133,806  
Cost of sales 57,108 61,415 105,592 117,332  
Earnings (losses) of unconsolidated operations 14,164 13,138 30,735 29,124  
Operating expenses (income) 31,633 20,009 51,479 37,967  
Operating (loss) profit (2,267) (51) 8,749 7,631  
Expenditures for property, plant and equipment and acquisition of mineral interests 8,491 3,142 41,921 11,950  
Depreciation, depletion and amortization 6,110 6,091 11,617 12,884  
 Total assets 677,487   677,487   $ 661,228
Operating segments | Utility Coal Mining          
Segment Reporting [Line Items]          
Revenues 21,477 28,626 38,168 47,865  
Cost of sales 21,104 30,327 37,054 52,897  
Earnings (losses) of unconsolidated operations 13,646 11,656 27,754 26,119  
Operating expenses (income) 7,739 8,733 15,164 16,074  
Operating (loss) profit 6,280 1,222 13,704 5,013  
Expenditures for property, plant and equipment and acquisition of mineral interests 497 1,433 1,030 2,050  
Depreciation, depletion and amortization 2,404 2,132 4,716 4,150  
 Total assets 120,118   120,118   125,715
Operating segments | Contract Mining          
Segment Reporting [Line Items]          
Revenues 36,919 30,723 69,558 62,249  
Cost of sales 32,045 28,659 59,789 57,037  
Earnings (losses) of unconsolidated operations 1,579 1,232 3,081 2,201  
Operating expenses (income) 2,688 2,286 5,097 4,433  
Operating (loss) profit 3,765 1,010 7,753 2,980  
Expenditures for property, plant and equipment and acquisition of mineral interests 6,780 1,032 18,612 7,786  
Depreciation, depletion and amortization 2,493 2,917 4,491 5,619  
 Total assets 231,292   231,292   213,571
Operating segments | Minerals and Royalties          
Segment Reporting [Line Items]          
Revenues 10,617 7,268 20,163 18,170  
Cost of sales 1,278 986 2,399 3,230  
Earnings (losses) of unconsolidated operations (1,061) 251 (100) 805  
Operating expenses (income) 1,530 1,328 3,180 2,633  
Operating (loss) profit 6,748 5,205 14,484 13,112  
Expenditures for property, plant and equipment and acquisition of mineral interests 1 0 70 807  
Depreciation, depletion and amortization 944 845 1,831 2,753  
 Total assets 111,338   111,338   115,545
Unallocated Items          
Segment Reporting [Line Items]          
Revenues 4,433 2,223 9,264 6,623  
Cost of sales 3,815 2,051 8,427 5,288  
Earnings (losses) of unconsolidated operations 0 (1) 0 (1)  
Operating expenses (income) 19,676 7,662 28,038 14,827  
Operating (loss) profit (19,058) (7,491) (27,201) (13,493)  
Expenditures for property, plant and equipment and acquisition of mineral interests 1,213 677 22,209 1,307  
Depreciation, depletion and amortization 269 197 579 362  
 Total assets 214,739   214,739   $ 206,397
Eliminations          
Segment Reporting [Line Items]          
Revenues (1,136) (605) (2,068) (1,101)  
Cost of sales (1,134) (608) (2,077) (1,120)  
Operating (loss) profit $ (2) $ 3 $ 9 $ 19