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Share-based compensation - Narrative (Details) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018
Disclosure of terms and conditions of share-based payment arrangement [line items] |  |
Number of shares reserved for future grants of stock options and share appreciation rights (in shares) | 4,311,729 |
Liabilities from share-based payment transactions | $ 18,382 | $ 52,794
SARs and TSARs |  |
Disclosure of terms and conditions of share-based payment arrangement [line items] |  |
Maximum term | 7 years |
Fair value of share-based payment transactions | $ 7,800 |
Liabilities from share-based payment transactions | 7,300 |
Intrinsic value of liabilities from share-based payment transactions | $ 500 |
Weighted average remaining vesting period | 1 year 7 months |
Expense from share-based payment transactions with employees | $ 8,700 | 1,200
Expense from share-based payment transactions with employees, effect of change in share price | $ 13,700 | 7,800
Vesting rate | 33.33% |
Performance Share Units (PSU) New Plan |  |
Disclosure of terms and conditions of share-based payment arrangement [line items] |  |
Maximum term | 3 years |
Deferred, Restricted and Performance Share Units |  |
Disclosure of terms and conditions of share-based payment arrangement [line items] |  |
Fair value of share-based payment transactions | $ 14,700 |
Liabilities from share-based payment transactions | 11,000 |
Intrinsic value of liabilities from share-based payment transactions | $ 3,700 |
Weighted average remaining vesting period | 1 year 11 months |
Expense from share-based payment transactions with employees | $ 4,500 | 5,100
Expense from share-based payment transactions with employees, effect of change in share price | $ 4,900 | 8,900
Stock Options |  |
Disclosure of terms and conditions of share-based payment arrangement [line items] |  |
Maximum term | 7 years |
Expense from share-based payment transactions with employees | $ 200 | $ 400
Minimum | Tranche 2 | Performance Share Units (PSU) New Plan |  |
Disclosure of terms and conditions of share-based payment arrangement [line items] |  |
Share-based compensation arrangement vesting rights, percentage | 0.00% |
Maximum | Tranche 2 | Performance Share Units (PSU) New Plan |  |
Disclosure of terms and conditions of share-based payment arrangement [line items] |  |
Share-based compensation arrangement vesting rights, percentage | 200.00% |

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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
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- Definition The amount of expense from share-based payment transactions with employees. + References 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 + Details
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- Definition The intrinsic value of liabilities arising from share-based transactions for which the counterparty's right to cash or other assets had vested by the end of the period (for example, vested share appreciation rights). The intrinsic value is the difference between the fair value of the shares to which the counterparty has the (conditional or unconditional) right to subscribe, or which it has the right to receive, and the price (if any) that the counterparty is (or will be) required to pay for those shares. Share-based payment transactions are transactions in which the entity: (a) receives goods or services from the supplier of those goods or services (including an employee) in a share-based payment arrangement; or (b) incurs an obligation to settle the transaction with the supplier in a share-based payment arrangement when another group entity receives those goods or services, for which the counterparty's right to cash or other assets had vested by the end of the period (for example, vested share appreciation rights). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2019-01-01 -Paragraph 51 -Subparagraph b -Clause ii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2019-en-r&anchor=para_51_b_ii&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The amount of liabilities arising from share-based payment transactions. Share-based payment transactions are transactions in which the entity: (a) receives goods or services from the supplier of those goods or services (including an employee) in a share-based payment arrangement; or (b) incurs an obligation to settle the transaction with the supplier in a share-based payment arrangement when another group entity receives those goods or services. [Refer: Share-based payment arrangements [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 2 -IssueDate 2019-01-01 -Paragraph 51 -Subparagraph b -Clause i -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=2&code=ifrs-tx-2019-en-r&anchor=para_51_b_i&doctype=Standard -URIDate 2019-03-27 + Details
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- Definition The number of shares reserved for issue under options and contracts for the sale of shares. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 1 -IssueDate 2019-01-01 -Paragraph 79 -Subparagraph a -Clause vii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2019-en-r&anchor=para_79_a_vii&doctype=Standard -URIDate 2019-03-27 + Details
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