Current and Long-Term Financing (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 15, 2026
Line of Credit Facility [Line Items]
Interest paid	$ 1,600,000	$ 1,400,000
Deferred financing fees	1,800,000
Outstanding notes payable	20,370,000	45,000,000
NACoal
Line of Credit Facility [Line Items]
Line of credit facility, amount outstanding	4,000,000	30,000,000
Line of credit facility, remaining borrowing capacity	116,231,000	116,951,000
Secured Debt | NACoal
Line of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	150,000,000
Line of credit facility, amount outstanding	4,000,000
Line of credit facility, remaining borrowing capacity	116,200,000
Amount of letters of credit outstanding	$ 29,800,000
Line of credit facility, unused capacity, commitment fee percentage	0.35%
Weighted average interest rate	4.50%
Fixed charge coverage ratio	1.10
Line of credit facility, availability required to pay dividends	$ 15,000,000
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	1.25%
Secured Debt | NACoal | LIBOR Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	2.25%
Secured Debt | Demand Note Payable to Unconsolidated Subsidiary | NACoal
Line of Credit Facility [Line Items]
Outstanding notes payable	$ 2,600,000	$ 4,400,000
Interest rate	0.18%	0.14%
Secured Debt | Notes Payable, Maturing At Various Dates Through 2027 | NACoal
Line of Credit Facility [Line Items]
Weighted average interest rate	4.03%
Outstanding notes payable	$ 13,800,000	$ 10,600,000
Secured Debt | Forecast | Notes Payable, Maturing December 2026 | NACoal
Line of Credit Facility [Line Items]
Principal payment due at maturity			$ 4,400,000