Prepaid expenses - Additional information (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Prepaid expenses
Non-current lease prepayments	$ 26,582	$ 27,464
Life of underlying assets	P35Y
Empresa de Generacion Huanza S.A. [Member]
Prepaid expenses
Non-current lease prepayments	$ 31,007,190,000

The amount of non-current prepayments for leases. [Refer: Non-current prepayments]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2019-01-01
-Paragraph 55
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_55&doctype=Standard
-URIDate 2019-03-27

Name:	ifrs-full_NoncurrentLeasePrepayments
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant