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REVENUE FROM CONTRACTS WITH CUSTOMERS - UNINSTALLED MATERIALS (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Sep. 30, 2020
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Revenue from Contract with Customer [Abstract] |  |
Uninstalled materials | $ 226 | $ 489

X
- Definition Uninstalled Materials, Current + References No definition available. + Details
Name: | brn_UninstalledMaterialsCurrent
Namespace Prefix: | brn_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_RevenueFromContractWithCustomerAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration