v3.26.3
Property, Plant and Equipment - Schedule of Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
Sep. 30, 2026
Dec. 31, 2025
Property, Plant, and Equipment [Line Items]    
Total Property, Plant and Equipment $ 9,057,693 $ 8,730,802
Less: Accumulated Depreciation, Depletion and Amortization 4,751,862 4,343,920
Total Property, Plant and Equipment—Net 4,305,831 4,386,882
Plant and Equipment    
Property, Plant, and Equipment [Line Items]    
Total Property, Plant and Equipment 5,141,618 4,876,926
Coal Properties and Surface Lands    
Property, Plant, and Equipment [Line Items]    
Total Property, Plant and Equipment 2,245,379 2,241,915
Mine Development    
Property, Plant, and Equipment [Line Items]    
Total Property, Plant and Equipment 690,642 690,845
Airshafts    
Property, Plant, and Equipment [Line Items]    
Total Property, Plant and Equipment 648,686 591,146
Advance Mining Royalties    
Property, Plant, and Equipment [Line Items]    
Total Property, Plant and Equipment $ 331,368 $ 329,970