Revenue Recognition (Disaggregation of Revenue) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Disaggregation of Revenue [Line Items]
Revenues	$ 214,794	$ 241,719
Goods transferred at a point in time
Disaggregation of Revenue [Line Items]
Revenues	83,273	92,842
Services transferred over time
Disaggregation of Revenue [Line Items]
Revenues	131,521	148,877
Operating Segments | Coal Mining customer
Disaggregation of Revenue [Line Items]
Revenues	85,415	95,204
Operating Segments | NAMining
Disaggregation of Revenue [Line Items]
Revenues	90,532	85,664
Operating Segments | Minerals Management lessee
Disaggregation of Revenue [Line Items]
Revenues	32,985	60,242
Unallocated Items
Disaggregation of Revenue [Line Items]
Revenues	8,459	2,952
Eliminations
Disaggregation of Revenue [Line Items]
Revenues	$ (2,597)	$ (2,343)