Inventories (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Materials and supplies	$ 108.0	$ 116.3
Raw coal	73.5	85.1
Saleable coal	138.2	130.1
Total	319.7	331.5
Material and supplies
Inventory [Line Items]
inventory reserves	9.6	7.9
Coal
Inventory [Line Items]
inventory reserves	$ 29.0	$ 8.3

Amount of valuation reserve for inventory.

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