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Derivative financial instruments - Interest Rate Swaps (Details) - Interest rate swaps - USD ($) $ in Millions | Mar. 12, 2019 | Dec. 31, 2018 | Dec. 31, 2016
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Not Designated As Hedging Instrument |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Notional amount of interest rate swaps |  |  | $ 100
Derivative fixed interest rate |  |  | 1.04%
Swap contract |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Financial assets, at fair value |  | $ 1 |
Entering into significant commitments or contingent liabilities | Not Designated As Hedging Instrument |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Notional amount of interest rate swaps | $ 125 |  |
Bottom of range | Entering into significant commitments or contingent liabilities | Not Designated As Hedging Instrument |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Derivative fixed interest rate | 2.36% |  |
Top of range | Entering into significant commitments or contingent liabilities | Not Designated As Hedging Instrument |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Derivative fixed interest rate | 2.67% |  |

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- Definition The fair value of financial assets. [Refer: At fair value [member]; Financial assets] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 7 -IssueDate 2017-01-01 -Paragraph 25 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=7&date=2017-03-01&anchor=para_25&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition Aggregate notional amount specified by the derivative(s). Expressed as an absolute value. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 12 -Section 13 -Sentence Column B + Details
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