XML 304 R92.htm IDEA: XBRL DOCUMENT v3.22.0.1
Business Segments (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Segment Reporting Information [Line Items]    
Revenues $ 191,846 $ 128,432
Operating profit (loss) 55,410 13,448
Expenditures for property, plant and equipment and acquisition of mineral interests 44,561 44,368
Depreciation, depletion and amortization 23,085 18,114
Operating Segments | Coal Mining customer    
Segment Reporting Information [Line Items]    
Revenues 91,851 72,088
Operating profit (loss) 49,059 25,436
Expenditures for property, plant and equipment and acquisition of mineral interests 16,830 14,825
Depreciation, depletion and amortization 16,649 14,213
Operating Segments | NAMining customer    
Segment Reporting Information [Line Items]    
Revenues 69,924 42,392
Operating profit (loss) 109 1,872
Expenditures for property, plant and equipment and acquisition of mineral interests 21,100 13,862
Depreciation, depletion and amortization 4,435 2,470
Operating Segments | Minerals Management    
Segment Reporting Information [Line Items]    
Revenues 31,003 14,721
Operating profit (loss) 26,080 3,493
Expenditures for property, plant and equipment and acquisition of mineral interests 6,423 15,474
Depreciation, depletion and amortization 1,858 1,308
Unallocated Items    
Segment Reporting Information [Line Items]    
Revenues 4,695 2,133
Operating profit (loss) (19,553) (17,256)
Expenditures for property, plant and equipment and acquisition of mineral interests 208 207
Depreciation, depletion and amortization 143 123
Eliminations    
Segment Reporting Information [Line Items]    
Revenues (5,627) (2,902)
Operating profit (loss) $ (285) $ (97)