Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 2,219.6	$ 2,141.4
Less: accumulated depreciation and depletion	(1,158.3)	(1,089.6)
Property, plant and equipment, net	1,061.3	1,051.8
Depreciation and depletion expense	75.6	75.4	$ 82.1
Mineral Rights and Reserves [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	545.9	547.8
Land [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	44.5	42.7
Buildings [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	199.6	195.6
Machinery and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,247.5	1,193.6
Furniture and Fixtures and Other [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	132.3	123.3
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 49.8	$ 38.4