Salaries and social security expenses - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Salaries and social security expenses [abstract]
Wages and salaries	$ 104,400	$ 105,931	$ 132,025
Social security costs	30,888	29,865	30,558
Equity-settled share-based compensation	4,734	4,728	5,552
Salaries and social security expenses	140,022	140,524	168,135
Wages and salaries capitalized in property, plant and equipment	$ 32,714	$ 32,636	$ 41,172

The amount of expense arising from equity-settled share-based payment transactions in which the goods or services received did not qualify for recognition as assets. [Refer: Expense from share-based payment transactions in which goods or services received did not qualify for recognition as assets]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 2
-IssueDate 2018-01-01
-Paragraph 51
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=2&date=2018-03-01&anchor=para_51_a&doctype=Standard
-URIDate 2018-03-16

Name:	ifrs-full_ExpenseFromEquitysettledSharebasedPaymentTransactionsInWhichGoodsOrServicesReceivedDidNotQualifyForRecognitionAsAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration