v3.26.1
Long-Term Debt - Credit Facility (Details) - USD ($)
$ in Millions
 6 Months Ended
Jan. 13, 2023
Jun. 30, 2026
Credit Agreement    
Debt Instrument [Line Items]    
Maximum borrowing capacity $ 425.0  
Increase of maximum borrowing capacity $ 100.0  
Interest rate (as a percent) 6.25%  
Letters of credit outstanding   $ 41.0
Debt available for borrowing   $ 305.5
Annual commitment fee percentage, undrawn portion   0.50%
Minimum debt to cash flow ratio for restriction to apply on cash distribution 1  
Minimum liquidity to extend maturity $ 200.0  
Interest coverage ratio 3  
Actual cash flow to interest expense ratio for trailing twelve months   41.98
Credit Agreement | Overnight Bank Funding Rate    
Debt Instrument [Line Items]    
Basis spread for variable interest rate (as a percent) 0.50%  
Credit Agreement | Daily Simple Secured Overnight Financing Rate    
Debt Instrument [Line Items]    
Basis spread for variable interest rate (as a percent) 1.00%  
Credit Agreement | Alliance Coal    
Debt Instrument [Line Items]    
Maximum Ratio of Debt to Cash Flow of Alliance Minerals 1.5  
Actual debt to cash flow ratio for trailing twelve months   0.37
Credit Agreement | Alliance Coal and Intermediate Partnership    
Debt Instrument [Line Items]    
Maximum Ratio of Debt to Cash Flow of Alliance Minerals 2.5  
Actual debt to cash flow ratio for trailing twelve months   1.16
Swingline subfacility    
Debt Instrument [Line Items]    
Maximum borrowing capacity $ 15.0  
Term loan    
Debt Instrument [Line Items]    
Maximum borrowing term loan $ 75.0  
Effective interest rate (as a percent)   7.23%