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Inventories (Details) - USD ($)
$ in Millions
Jun. 30, 2017
Dec. 31, 2016
Inventory Disclosure [Abstract]    
Finished goods $ 133.4 $ 151.7
Raw materials and precious metals 90.1 98.4
In-process inventories 18.9 23.9
Parts and supplies 75.9 75.2
Total Inventories $ 318.3 $ 349.2