Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 191,846	$ 128,432
Goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	80,515	68,073
Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	111,331	60,359
Operating Segments | Coal Mining customer
Disaggregation of Revenue [Line Items]
Revenues	91,851	72,088
Operating Segments | NAMining
Disaggregation of Revenue [Line Items]
Revenues	69,924	42,392
Operating Segments | Minerals Management lessee
Disaggregation of Revenue [Line Items]
Revenues	31,003	14,721
Unallocated Items
Disaggregation of Revenue [Line Items]
Revenues	4,695	2,133
Eliminations
Disaggregation of Revenue [Line Items]
Revenues	$ (5,627)	$ (2,902)