Current and Long-Term Financing (Narrative) (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) unitOfEquipment notePayable	Dec. 31, 2022 USD ($)	Dec. 15, 2026 USD ($)
Line of Credit Facility [Line Items]
Interest paid	$ 2,400,000	$ 2,000,000
Outstanding notes payable	35,844,000	18,900,000
NACoal
Line of Credit Facility [Line Items]
Revolving credit agreement		0
Line of credit facility, remaining borrowing capacity	105,120,000	$ 116,285,000
Secured Debt
Line of Credit Facility [Line Items]
Line of credit facility, average borrowing	6,200,000
Secured Debt | NACoal
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	150,000,000
Revolving credit agreement	10,000,000
Line of credit facility, remaining borrowing capacity	105,100,000
Amount of letters of credit outstanding	$ 34,900,000
Line of credit facility, unused capacity, commitment fee percentage	0.34%
Weighted average interest rate	6.06%	2.54%
Fixed charge coverage ratio	1.10
Line of credit facility, availability required to pay dividends	$ 15,000,000
Secured Debt | NACoal | Demand Note Payable to Unconsolidated Subsidiary
Line of Credit Facility [Line Items]
Outstanding notes payable	$ 7,000,000	$ 5,700,000
Interest rate	5.12%	3.36%
Secured Debt | NACoal | Notes Payable, Maturing At Various Dates Through 2029
Line of Credit Facility [Line Items]
Weighted average interest rate	5.42%
Outstanding notes payable	$ 18,800,000	$ 13,200,000
Number of notes payable | notePayable	11
Number of specified units of equipment | unitOfEquipment	16
Secured Debt | NACoal | Notes Payable, Maturing December 2026 | Forecast
Line of Credit Facility [Line Items]
Principal payment due at maturity			$ 4,400,000
Secured Debt | NACoal | Maximum
Line of Credit Facility [Line Items]
Maximum debt to EBITDA ratio	2.75
Maximum EBITDA ratio	1.50
Secured Debt | NACoal | Minimum
Line of Credit Facility [Line Items]
Minimum interest coverage ratio	4.00
Maximum EBITDA ratio	1.50
Secured Debt | NACoal | Base Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.23%
Secured Debt | NACoal | Secured Overnight Financing Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.23%