Property, plant and equipment - Commitments (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Disclosure of joint ventures [abstract]
Capital expenditure commitments	$ 15,635	$ 26,935

The amount of future capital expenditures that the entity is committed to make.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2019-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_112_c&doctype=Standard
-URIDate 2019-03-27

Name:	ifrs-full_CapitalCommitments
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant