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Use of Judgements and Estimates (Narrative) (Details)
 12 Months Ended
Dec. 31, 2017
$ / oz
$ / T
Gold Commodity Type [member]  
Disclosure Of Detailed Information About Use Of Judgements And Estimates Explanatory [line items]  
Long term prices used for reserves and resource estimates related to commodity per ounce | $ / oz 1,250
Silver Commodity Type [member]  
Disclosure Of Detailed Information About Use Of Judgements And Estimates Explanatory [line items]  
Long term prices used for reserves and resource estimates related to commodity per ounce | $ / oz 19
Lead Commodity [member]  
Disclosure Of Detailed Information About Use Of Judgements And Estimates Explanatory [line items]  
Long term prices used for reserves and resource estimates related to commodity per ounce | $ / T 2,200
Zinc Commodity [member]  
Disclosure Of Detailed Information About Use Of Judgements And Estimates Explanatory [line items]  
Long term prices used for reserves and resource estimates related to commodity per ounce | $ / T 2,500