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Reversal of Impairment and Goodwill - Key Assumptions and Sensitivity Analysis (Details)
 12 Months Ended
Dec. 31, 2017
$ / pure
$ / tonne
$ / Ounce
Dec. 31, 2016
$ / tonne
$ / Ounce
Disclosure of impairment loss and reversal of impairment loss [line items]    
Weighted average cost of capital, significant unobservable inputs, assets 5.20% 6.40%
Bottom of range [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Discount rate applied to cash flow projections 4.00% 5.00%
Top of range [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Discount rate applied to cash flow projections 9.00% 9.00%
Silver, Ounces    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts | $ / Ounce 18.50 18.50
Silver, Ounces | Weighted average [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts | $ / Ounce 18.57 19.93
Gold, Ounces    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts | $ / Ounce 1,300 1,300
Gold, Ounces | Weighted average [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts | $ / Ounce 1,307 1,327
Zinc [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 2,600 2,200
Zinc [member] | Weighted average [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 2,818 2,567
Copper [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 5,500 5,000
Copper [member] | Weighted average [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 6,742 5,725
Lead [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 2,200 2,000
Lead [member] | Weighted average [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 2,251 2,142
Option contract [member] | Zinc [member] | Bottom of range [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 2,609  
Option contract [member] | Zinc [member] | Top of range [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 3,555  
Option contract [member] | Copper [member] | Bottom of range [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 6,222  
Option contract [member] | Copper [member] | Top of range [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 7,277  
Option contract [member] | Lead [member] | Bottom of range [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 2,200  
Option contract [member] | Lead [member] | Top of range [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Metal prices used to calculate recoverable amounts 2,679