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Reversal of Impairment and Goodwill - Reversals of Impairment (Details)
$ in Thousands, Ounce in Millions
 12 Months Ended
Dec. 31, 2017
USD ($)
Ounce
Dec. 31, 2016
USD ($)
Disclosure of impairment loss and reversal of impairment loss [line items]    
Period of analyst consensus prices used for economic impairment modeling 4 years  
Reversals of impairment $ 61,554 $ 0
Reversal of impairment, net of tax 53,400  
Morococha mine [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Reversals of impairment 60,237 0
Reversal of impairment, net of tax $ 52,100  
Increase in silver mineral reserve | Ounce 2.8  
Calcatreu project [member]    
Disclosure of impairment loss and reversal of impairment loss [line items]    
Reversals of impairment $ 1,317 $ 0