DERIVATIVES AND HEDGING (Derivatives Designated as Hedging, by Balance Sheet Location) (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	$ 21,484	$ 29,058
Liability Derivatives, Fair Value	24,923	44,267
Derivative Assets, Amounts offsett in the Statement of Financial Condition	(2,295)	(13,929)
Derivative Asset, Subject to Master Netting Arrangement, Collateral, Obligation to Return Cash, Offset Against Derivative Asset	0	0
Derivative Liability, Subject to Master Netting Arrangement, Collateral, Right to Reclaim Cash Offset	7,644	529
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional/Contract Amount	444,197	442,739
Liability Derivatives, Notional/Contract Amount	471,877	479,975
Not Designated as Hedging Instrument [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	19,531	15,404
Not Designated as Hedging Instrument [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	30,315	30,036
Interest rate swaps [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	21,484	29,058
Liability Derivatives, Fair Value	24,923	44,267
Derivative Assets, Amounts offsett in the Statement of Financial Condition	(2,295)	(13,929)
Derivative Asset, Subject to Master Netting Arrangement, after Offset	(19,189)	(15,129)
Derivative Liability, Subject to Master Netting Arrangement, after Offset	30,272	29,809
Interest rate swaps [Member] \| Designated as Hedging Instrument [Member] \| Cash Flow Hedging
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional/Contract Amount	0	0
Liability Derivatives, Notional/Contract Amount	400,000	400,000
Interest rate swaps [Member] \| Designated as Hedging Instrument [Member] \| Other assets [Member] \| Cash Flow Hedging
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	0	0
Interest rate swaps [Member] \| Designated as Hedging Instrument [Member] \| Other liabilities [Member] \| Cash Flow Hedging
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	3,392	15,141
Interest rate swaps [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional/Contract Amount	386,724	416,711
Liability Derivatives, Notional/Contract Amount	386,724	416,711
Interest rate swaps [Member] \| Not Designated as Hedging Instrument [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	21,484	29,058
Interest rate swaps [Member] \| Not Designated as Hedging Instrument [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	21,531	29,126
Loan Participations and Assignments \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional/Contract Amount	875	1,050
Liability Derivatives, Notional/Contract Amount	43,541	45,298
Loan Participations and Assignments \| Not Designated as Hedging Instrument [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	0	0
Loan Participations and Assignments \| Not Designated as Hedging Instrument [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	28	42
Mortgage loan commitments [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional/Contract Amount	39,726	19,572
Liability Derivatives, Notional/Contract Amount	4,660	0
Mortgage loan commitments [Member] \| Not Designated as Hedging Instrument [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	341	275
Mortgage loan commitments [Member] \| Not Designated as Hedging Instrument [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	1	0
Forward Contracts [Member] \| Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Notional/Contract Amount	16,872	5,406
Liability Derivatives, Notional/Contract Amount	36,952	17,966
Forward Contracts [Member] \| Not Designated as Hedging Instrument [Member] \| Other assets [Member]
Derivatives, Fair Value [Line Items]
Asset Derivatives, Fair Value	1	0
Forward Contracts [Member] \| Not Designated as Hedging Instrument [Member] \| Other liabilities [Member]
Derivatives, Fair Value [Line Items]
Liability Derivatives, Fair Value	$ 14	$ 185

Fair value, after effect of master netting arrangement, of financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and contract can be net settled by means outside contract or delivery of asset. Includes derivative subject to master netting arrangement not elected or qualified to offset. Excludes derivative not subject to master netting arrangement or similar agreement.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483466/210-20-50-3

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-22

+ Details

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

- Definition

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 5
-SubTopic 10
-Topic 815
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480463/815-10-45-5

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-SubTopic 20
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483466/210-20-50-3

+ Details

Name:	us-gaap_DerivativeAssetCollateralObligationToReturnCashOffset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-SubTopic 20
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483466/210-20-50-3

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 55
-Paragraph 8
-SubTopic 20
-Topic 210
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-8

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5C
-Subparagraph (SX 210.12-13C(Column F))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5C

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5B
-Subparagraph (SX 210.12-13B(Column E))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5B

+ Details

Name:	us-gaap_DerivativeAssetFairValueGrossLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Nominal or face amount used to calculate payments on the derivative asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5
-Subparagraph (SX 210.12-13(Column A)(Footnote 3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5C
-Subparagraph (SX 210.12-13C(Column E))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5C

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5A
-Subparagraph (SX 210.12-13A(Column D))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5A

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5B
-Subparagraph (SX 210.12-13B(Column B))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5B

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

+ Details

Name:	us-gaap_DerivativeAssetNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4B
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-4B

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 22
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-22

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483466/210-20-50-3

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 7
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483444/210-20-55-7

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 4D
-Subparagraph (c)(2)
-SubTopic 20
-Topic 860
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481326/860-20-50-4D

+ Details

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

- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ References

+ Details

Name:	us-gaap_DerivativeFairValueOfDerivativeLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value, after effect of master netting arrangement, of financial liability or contract with one or more underlyings, notional amount or payment provision or both, and contract can be net settled by means outside contract or delivery of asset. Includes derivative subject to master netting arrangement not elected or qualified to offset. Excludes derivative not subject to master netting arrangement or similar agreement.

+ References

+ Details

Name:	us-gaap_DerivativeLiabilityAfterOffsetSubjectToMasterNettingArrangement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of right to receive cash collateral under master netting arrangements offset against derivative liabilities.

+ References

+ Details

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

- Definition

Nominal or face amount used to calculate payments on the derivative liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5C
-Subparagraph (SX 210.12-13C(Column E))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5C

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5
-Subparagraph (SX 210.12-13(Column D))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5A
-Subparagraph (SX 210.12-13A(Column D))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5A

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 320
-Name Accounting Standards Codification
-Section S99
-Paragraph 5B
-Subparagraph (SX 210.12-13B(Column A))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477271/946-320-S99-5B

Reference 5: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1B

Reference 6: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 1A
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480434/815-10-50-1A

+ Details

Name:	us-gaap_DerivativeLiabilityNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
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_DerivativesFairValueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_CashFlowHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_LoanParticipationsAndAssignmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=banr_MortgageLoanCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForwardContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: