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Commitments and contingencies - Narrative (Details) - t t in Millions | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018
Purchase commitment of methanol supply | Within one year |  |
Disclosure of associates [line items] |  |
Purchase commitments (in tonnes) | 1.2 |
Purchase commitment of methanol supply | Thereafter |  |
Disclosure of associates [line items] |  |
Purchase commitments (in tonnes) | 1.2 |
Atlas Joint Venture |  |
Disclosure of associates [line items] |  |
Percentage of marketing rights in production | 100.00% |
Percentage of ownership interest in associates | 63.10% | 63.10%
Atlas Joint Venture | Trinidad |  |
Disclosure of associates [line items] |  |
Percentage of ownership interest in associates | 63.10% |
Atlas Joint Venture | Egypt |  |
Disclosure of associates [line items] |  |
Percentage of ownership interest in associates | 50.00% |
Atlas Plant and Egypt Plant | Purchase commitment of methanol supply |  |
Disclosure of associates [line items] |  |
Purchase commitments (in tonnes) | 1.2 |

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