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Financial risk management (Details Textual) | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
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Disclosure Of Financial risk management [Line Items] |  |  |
Decrease in exchange rate basis points | (10.00%) | (10.00%) | (10.00%)
Bottom of range [member] | Foreign currency,increase [Member] |  |  |
Disclosure Of Financial risk management [Line Items] |  |  |
Closing foreign exchange rate | 3.602 |  |
Bottom of range [member] | Foreign currency,decrease [Member] |  |  |
Disclosure Of Financial risk management [Line Items] |  |  |
Closing foreign exchange rate | 2.947 |  |
Top of range [member] | Foreign currency,increase [Member] |  |  |
Disclosure Of Financial risk management [Line Items] |  |  |
Closing foreign exchange rate | 3.627 |  |
Top of range [member] | Foreign currency,decrease [Member] |  |  |
Disclosure Of Financial risk management [Line Items] |  |  |
Closing foreign exchange rate | 2.967 |  |

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- Definition The spot exchange rate at the end of the reporting period. Exchange rate is the ratio of exchange for two currencies. Spot exchange rate is the exchange rate for immediate delivery. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2017-01-01 -Paragraph 112 -Subparagraph c -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2017-03-01&anchor=para_112_c&doctype=Standard -URIDate 2017-03-09 + Details
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