PROPERTY, PLANT AND EQUIPMENT (Book Value of Land and Mineral Rights Disclosure) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Land Rights	$ 12.4	$ 12.4
Mineral Rights [Abstract]
Mineral Properties, Gross	537.2	537.2
Mineral Properties, Accumulated Depletion	(126.5)	(119.1)
Mineral Properties, Net	$ 410.7	$ 418.1

Amount before accumulated depletion of real estate held for productive use, excluding land held for sale.

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The accumulated decrease in the carrying value of the mineral properties as a result of mine or mineral production.

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Carrying amount at the balance sheet date of mineral properties, gross of adjustments.

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Mineral properties, net of adjustments.

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