Amount of 50% of Increment II post- threshold distributions received by KD

No definition available.

Name:	brn_A50ofIncrementIIDistributionsReceived
Namespace Prefix:	brn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Recognition of the difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee.

+ References

No definition available.

+ Details

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

- Definition

Cash Distribution from Equity Method Investment

+ References

No definition available.

+ Details

Name:	brn_CashDistributionfromEquityMethodInvestment
Namespace Prefix:	brn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Cumulative Cash Distributions from Kukio Resort Land Development Partnerships, Partial Payment Preferred Return

+ References

No definition available.

+ Details

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

- Definition

Cumulative Cash Distributions from Kukio Resort Land Development Partnerships, Preferred Return Made to Date

+ References

No definition available.

+ Details

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

- Definition

The cumulative cash distributions from Kukio Resort Land Development Partnerships (to all partners), made to date.

+ References

No definition available.

+ Details

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

- Definition

The cumulative cash distributions from Kukio Resort Land Development Partnerships, threshold, after which BHP receives a preferred return from KKM, up to $1M.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of limited liability limited partnerships formed through a wholly-owed subsidiary.

+ References

No definition available.

+ Details

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

- Definition

This element represents the aggregate cost of investments 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 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.12)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_EquityMethodInvestmentAggregateCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Difference between amount at which an investment accounted for under the equity method of accounting is carried (reported) on the balance sheet and amount of underlying equity in net assets the reporting Entity has in the investee.

+ 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)(3)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentDifferenceBetweenCarryingAmountAndUnderlyingEquity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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

Amount of income (loss) for proportionate share of equity method investee's income (loss).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(12))
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(10))
-URI http://asc.fasb.org/extlink&oid=116637232&loc=SL114874131-224263

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(13)(f))
-URI http://asc.fasb.org/extlink&oid=116637391&loc=SL114874048-224260

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 22
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=115929826&loc=d3e8736-108599

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=109237563&loc=d3e33749-111570

+ Details

Name:	us-gaap_IncomeLossFromEquityMethodInvestments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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

- Details

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

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=brn_IndirectlyAcquiredInterestMember
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_KDManiniowaliLLLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	dei_LegalEntityAxis=brn_KDKaupulehuLLLPMember
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_KaupulehuDevelopmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_StatementEquityComponentsAxis=us-gaap_NoncontrollingInterestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

INVESTMENTS - INVESTMENT IN KUKIO RESORT LAND DEVELOPMENT PARTNERSHIP (Details) $ in Thousands		1 Months Ended		3 Months Ended	12 Months Ended
	Nov. 27, 2013 USD ($) partnership	Aug. 31, 2020 USD ($)	Jun. 30, 2018 USD ($)	Dec. 16, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 07, 2019
Investment Holdings [Line Items]
Equity in income (loss) of affiliates					$ 352	$ (276)
Investments in land development partnerships
Investment Holdings [Line Items]
Number of limited liability limited partnerships formed \| partnership	2
Cumulative cash distributions from Kukio Resort land development partnerships, made to date					45,000
Cumulative cash distributions from Kukio Resort land development partnerships, partial payment preferred return		$ 197
Cash distribution from equity method investment					360	314
Equity in income (loss) of affiliates					352	(276)
Basis difference between the carrying amount and underlying equity					284
Basis difference adjustment					$ 13	18
Investments in land development partnerships \| Subsequent Event
Investment Holdings [Line Items]
Cumulative cash distributions from Kukio Resort land development partnerships, partial payment preferred return				$ 459
Cumulative cash distributions from Kukio Resort land development Partnerships, preferred return				656
Cash distribution from equity method investment				$ 1,034
KD Kukio Resorts LLLP \| Investments in land development partnerships
Investment Holdings [Line Items]
Ownership interest acquired	19.60%
Indirectly Acquired Interest \| Investments in land development partnerships
Investment Holdings [Line Items]
Aggregate cost	$ 5,140
KD Acquisition, LLLP \| Investments in land development partnerships
Investment Holdings [Line Items]
Ownership interest acquired					19.60%
KD Maniniowali, LLLP \| Investments in land development partnerships
Investment Holdings [Line Items]
Ownership interest acquired	19.60%
KD Kaupulehu, LLLP \| Investments in land development partnerships
Investment Holdings [Line Items]
Ownership interest acquired	19.60%
KD Kaupulehu, LLLP \| KD Acquisition II, LP \| Investments in land development partnerships
Investment Holdings [Line Items]
Ownership interest acquired							55.00%
Kaupulehu Developments \| KD Kaupulehu LLLP Increment II
Investment Holdings [Line Items]
50% of Increment II distributions received			$ 1,000
Replay \| KD Acquisition II, LP \| Investments in land development partnerships
Investment Holdings [Line Items]
Ownership interest acquired							45.00%
Barnwell Industries Inc \| KD Acquisition II, LP \| Investments in land development partnerships
Investment Holdings [Line Items]
Ownership interest acquired					10.80%
Non-controlling Interests \| Investments in land development partnerships
Investment Holdings [Line Items]
Cash distribution from equity method investment					$ 20	$ 38
Minimum \| Investments in land development partnerships
Investment Holdings [Line Items]
Cumulative cash distributions from Kukio Resort Land Development Partnerships, threshold	$ 45,000