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Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Disaggregation of Revenue [Line Items]    
Revenues $ 241,719 $ 191,846
Goods transferred at a point in time    
Disaggregation of Revenue [Line Items]    
Revenues 92,842 80,515
Services transferred over time    
Disaggregation of Revenue [Line Items]    
Revenues 148,877 111,331
Operating Segments | Coal Mining customer    
Disaggregation of Revenue [Line Items]    
Revenues 95,204 82,831
Operating Segments | NAMining    
Disaggregation of Revenue [Line Items]    
Revenues 85,664 78,944
Operating Segments | Minerals Management lessee    
Disaggregation of Revenue [Line Items]    
Revenues 60,242 31,003
Unallocated Items    
Disaggregation of Revenue [Line Items]    
Revenues 2,952 4,695
Eliminations    
Disaggregation of Revenue [Line Items]    
Revenues $ (2,343) $ (5,627)