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Property, Plant and Equipment - Summary of Key Assumptions Used for Assessing Recoverable Amount of Company's CGUs Versus Carrying Values (Detail) - Individual assets or cash-generating units [member]
 12 Months Ended
Dec. 31, 2017
$ / oz
$ / lb
Disclosure of detailed information about property, plant and equipment [line items]  
Gold price | $ / oz 1,300
Silver price | $ / oz 18
Lead price 1.09
Zinc price 1.27
Copper price 2.80
Bottom of range [member]  
Disclosure of detailed information about property, plant and equipment [line items]  
Discount rate 5.00%
Top of range [member]  
Disclosure of detailed information about property, plant and equipment [line items]  
Discount rate 8.00%