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Embedded derivatives (Details) - Sociedad Minera Cerro Verde S.A.A. [Member]
Number in Thousands
 12 Months Ended
Dec. 31, 2017
USD ($)
Number
Dec. 31, 2016
USD ($)
Number
Disclosure Of Embedded derivatives [Line Items]    
Embedded derivatives,maturity January 2018 to February 2018 January 2017 to February 2017
Forward pricing 8.950 5.542
Derivative financial asset liabilities $ 5,687,000 $ 319,000
Quantity of Metal | Number 3,340 3,455
Copper cathode [Member]    
Disclosure Of Embedded derivatives [Line Items]    
Embedded derivatives,maturity January 2018 January 2017
Forward pricing 3.274 2.507
Derivative financial asset liabilities $ 179,000 $ (1,000,000)
Quantity of Metal | Number 2,756 7,936
Copper concentrate [Member]    
Disclosure Of Embedded derivatives [Line Items]    
Embedded derivatives,maturity January 2018 to May 2018 January 2017 to May 2017
Derivative financial asset liabilities $ 62,870,000 $ 68,130,000
Quantity of Metal | Number 252,830 344,787
Bottom of range [member]    
Disclosure Of Embedded derivatives [Line Items]    
Provisional pricing $ 7.229 $ 5.431
Bottom of range [member] | Copper cathode [Member]    
Disclosure Of Embedded derivatives [Line Items]    
Provisional pricing 2.970 2.488
Bottom of range [member] | Copper concentrate [Member]    
Disclosure Of Embedded derivatives [Line Items]    
Provisional pricing $ 2.903 $ 2.091
Forward pricing 3.274 2.507
Top of range [member]    
Disclosure Of Embedded derivatives [Line Items]    
Provisional pricing $ 7.231 $ 5.484
Top of range [member] | Copper cathode [Member]    
Disclosure Of Embedded derivatives [Line Items]    
Provisional pricing 3.246 2.678
Top of range [member] | Copper concentrate [Member]    
Disclosure Of Embedded derivatives [Line Items]    
Provisional pricing $ 3.166 $ 2.656
Forward pricing 3.297 2.512