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Financial Risk Management - Additional Information (Detail)
$ / T in Thousands, $ in Thousands
 12 Months Ended
Dec. 31, 2017
USD ($)
$ / T
T
Dec. 31, 2016
Disclosure of risk management [line items]    
Increase/decrease in the U.S. dollar exchange rate against all currencies except Canadian dollar, Australian dollar, Euro, Turkish lira, Chinese renminbi, Swedish krona, Romanian lei, Great British pound and Brazilian real 1.00%  
Decrease/increase in profit (loss) before taxes due to 1% increase/decrease in the U.S. dollar exchange rate against all currencies except Canadian dollar, Australian dollar, Euro, Turkish lira, Chinese renminbi, Swedish krona, Romanian lei, Great British pound and Brazilian real $ 25  
Decrease/increase in other comprehensive income due to 1% increase/decrease in the U.S. dollar exchange rate against all currencies except Canadian dollar, Australian dollar, Euro, Turkish lira, Chinese renminbi, Swedish krona, Romanian lei, Great British pound and Brazilian real $ 0  
Debt fixed interest rate 6.13%  
Payment for metal sales period description Payment for metal sales is normally in advance or within fifteen days of shipment depending on the buyer.  
Number of days from shipment 15 days  
Debt to capital ratio 13.80% 14.00%
Net Debt to EBITDA ratio 0.9 (1.7)
Level 2 [member]    
Disclosure of risk management [line items]    
Derivative liability $ 837  
Lead [member]    
Disclosure of risk management [line items]    
Fair value hedge minimum price | $ / T 2,300  
Hedge per tonne | T 15,336  
Zinc [member]    
Disclosure of risk management [line items]    
Fair value hedge minimum price | $ / T 2,850  
Hedge per tonne | T 25,416  
Top of range [member]    
Disclosure of risk management [line items]    
Target debt to capital ratio less than 30% 30.00%  
Net Debt to EBITDA target ratio 3.5