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Financial Instruments - Additional Information (Details)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
USD ($)
buyer
Dec. 31, 2017
USD ($)
Disclosure of detailed information about financial instruments [line items]    
Trade and other receivables $ 96,091 $ 109,746
Allowance account for credit losses of financial assets 7,600 7,600
Gains (losses) on MXN derivative contracts 4,930 606
Minimum finance lease payments payable, at present value $ 6,676 $ 7,559
Interest rate on borrowings (percent) 1.80%  
Interest earned on cash and short-term investments (percent) 0.90% 0.77%
Impact of 10% change in interest earned on earnings before taxes $ 200 $ 200
Impact of 10% increase in metal prices on revenues 81,200 83,900
Impact of 10% decrease in metal prices on revenues 82,700 85,300
Impact of 10% increase in metal prices on earnings before taxes 6,200 7,400
Impact of 10% decrease in metal prices on earnings before taxes 6,200 7,400
Production Concentration Risk [member]    
Disclosure of detailed information about financial instruments [line items]    
Value contained in precious metal inventory at refineries 19,700 21,900
Credit risk [member]    
Disclosure of detailed information about financial instruments [line items]    
Current advances to suppliers 14,400 14,300
Currency risk [member]    
Disclosure of detailed information about financial instruments [line items]    
Gains (losses) on MXN derivative contracts 700 (3,800)
Effect of 10% change in exchange rate on income before taxes $ 14,300 $ 17,400
Interest rate risk [member]    
Disclosure of detailed information about financial instruments [line items]    
Interest rate on borrowings (percent) 2.20% 2.20%
Trade receivables from provisional concentrate sales [member] | Customer Concentration Risk [member]    
Disclosure of detailed information about financial instruments [line items]    
Trade and other receivables $ 40,800 $ 52,000
Number of well-known concentrate buyers | buyer 6