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Financial instruments and risk management - Credit risk - Additional information (Detail) - Credit risk [Member] - Customer | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017
Disclosure Of Financial Instruments [Line Items] |  |
Description of customers receivable owing | The Group had approximately 113 customers (2017: 115 customers) that owed the Group more than US$5 million each and these balances accounted for approximately 84% (2017: 78%) of all trade receivables. There were 17 customers (2017: 23 customers) with balances greater than US$20 million accounting for just over 34% (2017: 35%) of all trade receivables. |
More than US dollar 5 million [member] |  |
Disclosure Of Financial Instruments [Line Items] |  |
Number of customers | 113 | 115
Per cent of trade receivables | 84.00% | 78.00%
Greater than US dollar 20 million [member] |  |
Disclosure Of Financial Instruments [Line Items] |  |
Number of customers | 17 | 23
Per cent of trade receivables | 34.00% | 35.00%

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- Definition The description of the judgements, and changes in the judgements, that significantly affect the determination of the amount and timing of revenue from contracts with customers. [Refer: Revenue from contracts with customers] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Note Effective 2018-01-01 -Name IFRS -Number 15 -IssueDate 2017-01-01 -Paragraph 123 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2017-03-01&anchor=para_123&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition Number of customers. + References No definition available. + Details
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- Definition Percentage of receivable. + References No definition available. + Details
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- Details
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- Details
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