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Segment reporting - Major customers (Details) $ in Thousands | 12 Months Ended
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Dec. 31, 2018 USD ($) customer | Dec. 31, 2017 USD ($) customer | Dec. 31, 2016 USD ($) customer
Disclosure of major customers [abstract] |  |  |  |  |
Sales | $ 2,274,038 | $ 1,741,693 | [1] | $ 1,576,037 | [1]
Number of major customers | 0 |  |  |  |
Top Ten Customers [Member] |  |  |  |  |
Disclosure of major customers [abstract] |  |  |  |  |
Sales | $ 758,894 | $ 820,897 |  | $ 656,907 |
Number of major customers | customer | 10 | 10 |  | 10 |
Dow Corning Corporation [Member] |  |  |  |  |
Disclosure of major customers [abstract] |  |  |  |  |
Percentage of Company's sales |  | 12.20% |  | 13.70% |
[1] | The amounts for 2016 have been re-presented to show the results of the Spanish energy business within profit (loss) from continuing operations, as described in Note 1 to the consolidated financial statements.

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- Definition Represents the number of customers in the group used to measure and analyse concentration risk. + References No definition available. + Details
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- References No definition available. + Details
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- Definition The percentage of the entity's revenue. [Refer: Revenue] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IFRS -Number 8 -IssueDate 2018-01-01 -Paragraph 34 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=8&date=2018-03-01&anchor=para_34&doctype=Standard -URIDate 2018-03-16 + Details
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- Definition The amount of revenue from contracts with customers. A customer is a party that has contracted with an entity to obtain goods or services that are an output of the entity’s ordinary activities in exchange for consideration. [Refer: Revenue] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 15 -IssueDate 2018-01-01 -Paragraph 113 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_113_a&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 15 -IssueDate 2018-01-01 -Paragraph 114 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_114&doctype=Standard -URIDate 2018-03-16 + Details
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- Details
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- Details
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