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Financial - risk management objectives and policies (Details 1) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure of financial risk management objectives and policies [Line Items] |  |  |
Increase in libor iterest rate | 10.00% | 10.00% | 10.00%
Decrease in libor interest rate | (10.00%) | (10.00%) | (10.00%)
Libor interest rate increased effect on income | $ (677) | $ 333 | $ 294
Libor interest rate decreased effect on income | $ 677 | $ (333) | $ (294)

X
- Definition The percentage of decrease in libor interest rate. + References No definition available. + Details
Name: | cik0001013131_DecreaseInLiborInterestRate
Namespace Prefix: | cik0001013131_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- References No definition available. + Details
Name: | cik0001013131_DisclosureOfFinancialRiskManagementObjectivesAndPoliciesLineItems
Namespace Prefix: | cik0001013131_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The percentage of increase in libor interest rate. + References No definition available. + Details
Name: | cik0001013131_IncreaseInLiborIterestRate
Namespace Prefix: | cik0001013131_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition The amount of decrease in income due to decrease the libor interest rate. + References No definition available. + Details
Name: | cik0001013131_LiborInterestRateDecreasedEffectOnIncome
Namespace Prefix: | cik0001013131_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition The amount of increase in income due to Increase the libor interest rate. + References No definition available. + Details
Name: | cik0001013131_LiborInterestRateIncreasedEffectOnIncome
Namespace Prefix: | cik0001013131_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration