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Current and Long-Term Financing (Narrative) (Details) - USD ($)
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 15, 2026
Line of Credit Facility [Line Items]      
Interest paid $ 2,000,000 $ 1,600,000  
Deferred financing fees   1,800,000  
Line of credit facility, average borrowing 2,000,000    
Outstanding notes payable 18,873,000 20,400,000  
NACoal      
Line of Credit Facility [Line Items]      
Revolving credit agreement 0 4,000,000  
Line of credit facility, remaining borrowing capacity 116,285,000 $ 116,231,000  
Secured Debt | NACoal      
Line of Credit Facility [Line Items]      
Line of credit facility, maximum borrowing capacity 150,000,000    
Revolving credit agreement 0    
Line of credit facility, remaining borrowing capacity 116,300,000    
Amount of letters of credit outstanding $ 33,700,000    
Line of credit facility, unused capacity, commitment fee percentage 0.34%    
Weighted average interest rate 2.54% 4.50%  
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 $ 5,700,000 $ 2,600,000  
Interest rate 3.36% 0.18%  
Secured Debt | NACoal | Notes Payable, Maturing At Various Dates Through 2027      
Line of Credit Facility [Line Items]      
Weighted average interest rate 4.11%    
Outstanding notes payable $ 13,200,000 $ 13,800,000  
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 | LIBOR Rate      
Line of Credit Facility [Line Items]      
Basis spread on variable rate 2.23%