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Inventories (Details) - USD ($)
$ in Millions
Sep. 30, 2025
Dec. 31, 2024
Inventory [Line Items]    
Materials and supplies, net $ 164.3 $ 157.5
Raw coal 82.4 109.6
Saleable coal 158.5 126.3
Inventories, net $ 405.2 $ 393.4