Inventories (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Inventory [Line Items]
Materials and supplies	$ 102.6	$ 116.3
Raw coal	70.5	85.1
Saleable coal	88.5	130.1
Inventories	261.6	331.5
Material And Supplies
Inventory [Line Items]
Inventory reserves	10.4	7.9
Coal
Inventory [Line Items]
Inventory reserves	$ 7.6	$ 8.3

Amount of valuation reserve for inventory.

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