RELATED PARTY TRANSACTIONS (Details) $ in Thousands	12 Months Ended
Sep. 30, 2021 USD ($) lot	Sep. 30, 2020 USD ($) lot
Gros Ventre Partners, LLC
Related party transactions
Profit sharing ratio of variable interest entity	2.00%
Asset management fee, percent fee of cumulative capital contributions	1.00%
Kaupulehu Developments
Related party transactions
Revenues - sale of interest in leasehold land	$ 1,738	$ 325
Kaupulehu Developments \| KD Kaupulehu, LLLP \| Investments in land development partnerships \| Increment I
Related party transactions
Revenues - sale of interest in leasehold land	$ 1,738	$ 325
Number of single family lots sold \| lot	8	2
Four Pines Operating LLC \| Gros Ventre Partners, LLC
Related party transactions
Interest owned by member of Board of Directors	25.00%
KD Acquisition, LLLP \| Investments in land development partnerships
Related party transactions
Ownership interest acquired	19.60%
KD Acquisition II, LP \| Barnwell Industries Inc \| Investments in land development partnerships
Related party transactions
Ownership interest acquired	10.80%

Asset Management Fee, Percent Fee of Cumulative Capital Contributions

No definition available.

Name:	brn_AssetManagementFeePercentFeeOfCumulativeCapitalContributions
Namespace Prefix:	brn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the number of single-family lots sold.

+ References

No definition available.

+ Details

Name:	brn_NumberOfSingleFamilyLotsSold
Namespace Prefix:	brn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the profit sharing percentage between BOK and Gros Ventre

+ References

No definition available.

+ Details

Name:	brn_ProfitSharingRatioOfVariableInterestEntity
Namespace Prefix:	brn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Revenue from the sale of interest in leasehold land.

+ References

No definition available.

+ Details

Name:	brn_RevenuefromSaleofInterestinLeaseholdLand
Namespace Prefix:	brn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByNoncontrollingOwners
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=brn_GrosVentrePartnersLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=brn_KaupulehuDevelopmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=brn_KDKaupulehuLLLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=brn_LandDevelopmentPartnershipsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	brn_IncrementAxis=brn_IncrementIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=brn_FourPinesOperatingLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=brn_GrosVentrePartnersLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=brn_KDAcquisitionLLLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=brn_KDAcquisitionIILPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=brn_BarnwellIndustriesIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: