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Inventory (Narrative) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Disclosure of inventories [Abstract]    
Long-term inventory $ 68.7 $ 75.8
Mining and processing costs, inventories 323.3 304.1
Amortization costs, Inventories $ 125.6 $ 119.0