Salaries and social security expenses - Summary (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Salaries and social security expenses [abstract]
Wages and salaries	$ 89,662	$ 104,400	$ 105,931
Social security costs	27,430	30,888	29,865
Equity-settled share-based compensation	4,316	4,734	4,728
Salaries and social security expenses	121,408	140,022	140,524
Wages and salaries capitalized in property, plant and equipment	$ 27,544	$ 32,714	$ 32,636

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 2020-01-01
-Paragraph 51
-Subparagraph a
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2020-en-r&anchor=para_51_a&doctype=Standard
-URIDate 2020-01-01

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