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Investment in associate - Additional information (Details) - t t in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017
Atlas Methanol Company Unlimited |  |
Disclosure of associates [line items] |  |
Annual methanol production facility owned (in tonnes) | 1.8 |
Atlas Methanol Company Unlimited | Fixed-price contracts | Methanol | 2005 through 2014 |  |
Disclosure of associates [line items] |  |
Percentage of sales | 50.00% |
Atlas Methanol Company Unlimited | Fixed-price contracts | Methanol | Late 2014 through 2019 |  |
Disclosure of associates [line items] |  |
Percentage of sales | 10.00% |
Atlas Methanol Company Unlimited |  |
Disclosure of associates [line items] |  |
Percentage of ownership interest in associates | 63.10% | 63.10%

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- Definition The proportion of ownership interest in an associate attributable to the entity. [Refer: Associates [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2017-01-01 -Paragraph 17 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_17_b_iii&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2017-01-01 -Paragraph 16 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_16_b_iii&doctype=Standard -URIDate 2017-03-09 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2017-01-01 -Paragraph 21 -Subparagraph a -Clause iv -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_21_a_iv&doctype=Standard -URIDate 2017-03-09 + Details
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