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Significant accounting policies - Application of new and revised accounting standards (Details) - USD ($) $ in Thousands |  | 12 Months Ended |
--- | --- | --- | ---
Jan. 01, 2019 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of expected impact of initial application of new standards or interpretations [line items] |  |  |
Non-current assets |  | $ 3,964,094 | $ 3,356,923
Retained earnings |  | 1,039,819 | 1,145,476
Weighted average lessee's incremental borrowing rate applied to lease liabilities recognised at date of initial application of IFRS 16 | 4.40% |  |
Recognition exception for: |  |  |
Short-term leases |  | $ (500) |
Lease liabilities at January 1, 2019 | $ 452,882 |  |
IFRS 16, Leases |  |  |
Disclosure of expected impact of initial application of new standards or interpretations [line items] |  |  |
Non-current assets | 411,000 |  |
Total liabilities | 453,000 |  |
Retained earnings | 42,000 |  |
Retained earnings, net of tax | $ 38,000 |  |
Weighted average lessee's incremental borrowing rate applied to lease liabilities recognised at date of initial application of IFRS 16 | 4.40% |  |
Gross lease liabilities |  |  | $ 427,289
Recognition exception for: |  |  |
Short-term leases | $ (777) |  |
Leases of low-value assets | (8) |  |
Extension and termination options reasonably certain to be exercised | 75,753 |  |
Scope changes due to IFRS 16 | 18,880 |  |
Other | 594 |  |
Lease liabilities at January 1, 2019 | $ 358,440 |  |

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- Definition The amount of the expense relating to short-term leases accounted for applying paragraph 6 of IFRS 16. This expense need not include the expense relating to leases with a lease term of one month or less. Short-term lease is a lease that, at the commencement date, has a lease term of 12 months or less. A lease that contains a purchase option is not a short-term lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 16 -IssueDate 2019-01-01 -Paragraph 53 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2019-en-r&anchor=para_53_c&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of contractual undiscounted cash flows in relation to lease liabilities before deducting finance charges. [Refer: Lease liabilities] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 16 -IssueDate 2019-01-01 -Paragraph 58 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2019-en-r&anchor=para_58&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 7 -IssueDate 2019-01-01 -Paragraph B11D -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2019-en-r&anchor=para_B11D_a&doctype=Appendix&subtype=B -URIDate 2019-03-27 + Details
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- Definition Expiry date 2020-01-01: The amount of present obligations of the entity arising from past events, the settlement of which is expected to result in an outflow from the entity of resources embodying economic benefits. Effective 2020-01-01: The amount of a present obligation of the entity to transfer an economic resource as a result of past events. Economic resource is a right that has the potential to produce economic benefits. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 13 -IssueDate 2019-01-01 -Paragraph 93 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2019-en-r&anchor=para_93_a&doctype=Standard -URIDate 2019-03-27 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 13 -IssueDate 2019-01-01 -Paragraph 93 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2019-en-r&anchor=para_93_b&doctype=Standard -URIDate 2019-03-27 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 13 -IssueDate 2019-01-01 -Paragraph 93 -Subparagraph e -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=13&code=ifrs-tx-2019-en-r&anchor=para_93_e&doctype=Standard -URIDate 2019-03-27 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2019-01-01 -Paragraph 28 -Subparagraph d -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2019-en-r&anchor=para_28_d&doctype=Standard -URIDate 2019-03-27 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 8 -IssueDate 2019-01-01 -Paragraph 23 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=8&code=ifrs-tx-2019-en-r&anchor=para_23&doctype=Standard -URIDate 2019-03-27 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 55 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_55&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The weighted average lessee's incremental borrowing rate applied to lease liabilities recognised in the statement of financial position at the date of initial application of IFRS 16. The incremental borrowing rate is the rate of interest that a lessee would have to pay to borrow over a similar term, and with a similar security, the funds necessary to obtain an asset of a similar value to the right-of-use asset in a similar economic environment. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 16 -IssueDate 2019-01-01 -Paragraph C12 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2019-en-r&anchor=para_C12_a&doctype=Appendix&subtype=C -URIDate 2019-03-27 + Details
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