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Prepaid expenses (Details Textual) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Disclosure of Prepaid expenses [Line Items]    
Non-current lease prepayments [1] $ 27,464 $ 28,349
Life of underlying assets 35 year​​​​​​​s  
Empresa de Generacion Huanza S.A. [Member]    
Disclosure of Prepaid expenses [Line Items]    
Non-current lease prepayments $ 31,000  
[1] This item corresponds to the balance of an original prepayment of US$31 million for the lease of hydraulic installations by the subsidiary Empresa de Generacion Huanza S.A. This prepayment is being charged to results during the life of the underlying assets (35 years) since January 2015.