v3.25.4
Summary of Significant Accounting Policies (Narrative) (Details)
 12 Months Ended
Dec. 31, 2025
USD ($)
Dec. 31, 2024
USD ($)
Dec. 31, 2023
USD ($)
Mar. 31, 2016
USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Aggregate impact of foreign currency transaction gain (loss) $ 6,200,000 $ 21,600,000 $ 2,500,000  
Cash equivalents 106,900,000 221,400,000    
Restricted cash 300,000 300,000    
Interest capitalized 0 0    
Advance mining royalties 5,700,000 9,800,000    
Goodwill 28,008,000 28,008,000    
Derivative Notional Amount 80,000,000.0      
Impairment of assets 0 10,585,000 0  
Goodwill impairment $ 0 0    
Buchanan [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Goodwill       $ 28,000,000.0
CHESS Depositary Interests [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Share equivalent ratio 10      
Machinery, Mining Equipment And Transportation Vehicles [Member] | Maximum [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Property plant and equipment, useful life 10 years      
Machinery, Mining Equipment And Transportation Vehicles [Member] | Minimum [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Property plant and equipment, useful life 3 years      
Office Equipment [Member] | Maximum [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Property plant and equipment, useful life 10 years      
Office Equipment [Member] | Minimum [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Property plant and equipment, useful life 5 years      
Plant, Buildings And Improvements [Member] | Maximum [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Property plant and equipment, useful life 20 years      
Plant, Buildings And Improvements [Member] | Minimum [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Property plant and equipment, useful life 10 years      
US Dollar Coal Sales In Australia [Member]        
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Aggregate impact of foreign currency transaction gain (loss) $ (8,800,000) $ 8,400,000 $ (1,000,000.0)