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Revenue (Schedule of Disaggregation of Revenue) (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Disclosure of disaggregation of revenue from contracts with customers [line items]        
Gross revenue $ 17,129 $ 13,689 $ 68,100 $ 54,353
Treatment and selling costs (5,395) (3,875) (18,632) (12,119)
Revenue 11,734 9,814 49,468 42,234
Silver [Member]        
Disclosure of disaggregation of revenue from contracts with customers [line items]        
Provisional sales revenue 4,563 5,813 16,501 23,986
Derivative pricing adjustments (298) 151 (343) 1,466
Gross revenue 4,265 5,964 16,158 25,452
Zinc [Member]        
Disclosure of disaggregation of revenue from contracts with customers [line items]        
Provisional sales revenue 8,941 1,406 32,104 7,655
Derivative pricing adjustments (2,494) 330 (2,726) 544
Gross revenue 6,447 1,736 29,378 8,199
Lead [Member]        
Disclosure of disaggregation of revenue from contracts with customers [line items]        
Provisional sales revenue 6,785 5,475 22,641 18,461
Derivative pricing adjustments (489) 213 (440) 312
Gross revenue 6,296 5,688 22,201 18,773
Other by-products [Member]        
Disclosure of disaggregation of revenue from contracts with customers [line items]        
Provisional sales revenue 133 300 360 1,927
Derivative pricing adjustments (12) 1 3 2
Gross revenue $ 121 $ 301 $ 363 $ 1,929