Property, Plant and Equipment, Net (Details) (USD $)
In Millions, unless otherwise specified
Sep. 30, 2014
Dec. 31, 2013
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 1,332.7 $ 1,287.0
Less accumulated depreciation and depletion (641.4) (609.7)
Total property, plant and equipment, net 691.3 677.3
Land, Buildings and Structures and Leasehold Improvements [Member]
   
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 346.1 347.1
Machinery and Equipment [Member]
   
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 677.4 668.0
Office Furniture and Equipment [Member]
   
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 23.3 21.5
Mineral Interests [Member]
   
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 182.2 180.9
Construction in Progress [Member]
   
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 103.7 $ 69.5