Property, Plant and Equipment, Net (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 1,399.5	$ 1,327.3
Less accumulated depreciation and depletion	(636.6)	(626.4)
Property, plant and equipment, net	762.9	700.9
Land, Buildings and Structures and Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	347.3	352.2
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	696.7	669.1
Office Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	19.6	17.5
Mineral Interests [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	171.7	179.6
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 164.2	$ 108.9