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Inventories (Details) - USD ($)
$ in Millions
Sep. 30, 2022
Dec. 31, 2021
Inventory Disclosure [Abstract]    
Materials and supplies, net $ 121.7 $ 102.1
Raw coal 58.5 54.6
Saleable coal 97.2 70.0
Inventories, net 277.4 226.7
Material and supplies    
Inventory [Line Items]    
inventory reserves $ 7.6 $ 9.0