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Significant accounting principles and policies (Details Textual)
$ in Millions
Jan. 01, 2019
USD ($)
Dec. 31, 2018
Dec. 31, 2017
Property, Plant and Equipment [Member]      
DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory [Line Items]      
Right-of-use assets $ 96.8    
Other financial liabilities [Member]      
DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory [Line Items]      
Lease liabilities $ 95.7    
Written put options [member]      
DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory [Line Items]      
Closing foreign exchange rate   0.2959 0.3082
Purchased call options [member]      
DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory [Line Items]      
Closing foreign exchange rate   0.2968 0.3088
Sociedad Minera Cerro Verde S.A.A. [Member] | Written put options [member]      
DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory [Line Items]      
Closing foreign exchange rate   3.379 3.245
Sociedad Minera Cerro Verde S.A.A. [Member] | Purchased call options [member]      
DisclosureOfSummaryOfSignificantAccountingPoliciesExplanatory [Line Items]      
Closing foreign exchange rate   3.369 3.238