v3.26.1
Unconsolidated Subsidiaries (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Variable Interest Entity [Line Items]          
Variable interest entity, reporting entity involvement, maximum risk of loss $ 5,400   $ 5,400   $ 6,700
Earnings of unconsolidated operations 14,164 $ 13,138 30,735 $ 29,124  
Utility Coal Mining and Contract Mining Member          
Variable Interest Entity [Line Items]          
Earnings of unconsolidated operations $ 15,200 $ 12,900 $ 30,800 $ 28,300  
Unconsolidated Subsidiaries          
Variable Interest Entity [Line Items]          
Ownership (percent) 100.00%   100.00%    
Income from equity method investee $ 14,792   $ 14,792   14,750
Location, Statement of Financial Position, Balance [Axis]: us-gaap:OtherAssetsNoncurrent          
Variable Interest Entity [Line Items]          
Income from equity method investee $ 14,800   $ 14,800   $ 14,800