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Mineral Properties, Plant and Equipment - Additional Information (Details) - USD ($)
 12 Months Ended
May 18, 2018
Jan. 31, 2018
Dec. 31, 2018
Dec. 31, 2017
Disclosure of detailed information about property, plant and equipment [line items]        
Additions     $ 149,020,000 $ 148,102,000
Reversals of impairment     (27,789,000) 61,554,000
Gains on sale of mineral properties, plant and equipment (Note 11)     7,973,000 191,000
Calcatreu project [member]        
Disclosure of detailed information about property, plant and equipment [line items]        
Reversals of impairment     0 $ 1,317,000
Other disposals of assets [member] | Minera Aquiline Argentina SA [Member]        
Disclosure of detailed information about property, plant and equipment [line items]        
Percent of shares of Minera Aquiline Argentina SA sold (percent)   100.00%    
Consideration for held-for-sale assets sold   $ 15,000,000    
Proceeds from disposal of non-current assets or disposal groups classified as held for sale and discontinued operations $ 10,000,000 $ 5,000,000    
Gains on sale of mineral properties, plant and equipment (Note 11)     8,000,000  
Gain on disposals of property, plant and equipment, net of tax expense     $ 6,000,000