LOANS RECEIVABLE AND THE ALLOWANCE FOR CREDIT LOSSES (Allowance for Loan Losses) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision for credit losses	$ (4,549)	$ (1,424)
Recoveries	931	2,451
Charge-offs	(3,678)	(2,378)
Financing Receivable, Allowance for Credit Loss	157,323	151,140	$ 155,521	$ 149,643
Commercial Real Estate
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision for credit losses	(811)	(2,218)
Recoveries	57	1,389
Charge-offs	0	0
Financing Receivable, Allowance for Credit Loss	40,076	43,555	40,830	44,384
Multifamily Real Estate
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision for credit losses	(199)	(33)
Recoveries	0	0
Charge-offs	0	0
Financing Receivable, Allowance for Credit Loss	10,109	9,293	10,308	9,326
Construction and Land
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision for credit losses	(3,004)	(813)
Recoveries	0	0
Charge-offs	0	0
Financing Receivable, Allowance for Credit Loss	32,042	28,908	29,038	28,095
Commercial Business and Small Business Scored
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision for credit losses	(2,798)	(1,108)
Recoveries	557	781
Charge-offs	(3,301)	(1,809)
Financing Receivable, Allowance for Credit Loss		35,544	38,611	35,464
Agricultural Business
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision for credit losses	(96)	(81)
Recoveries	10	106
Charge-offs	0	0
Financing Receivable, Allowance for Credit Loss	5,641	3,890	5,727	3,865
One- to Four-Family Residential
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision for credit losses	(230)	(1,145)
Recoveries	188	16
Charge-offs	(13)	0
Financing Receivable, Allowance for Credit Loss	20,752	20,432	20,807	19,271
Consumer Loan [Member]
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Provision for credit losses	(83)	(690)
Recoveries	119	159
Charge-offs	(364)	(569)
Financing Receivable, Allowance for Credit Loss	10,038	$ 9,518	$ 10,200	$ 9,238
Commercial Business
Financing Receivable, Allowance for Loan Losses [Roll Forward]
Charge-offs	(2,915)
Financing Receivable, Allowance for Credit Loss	$ 38,665

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-11B

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph c
-Publisher SEC

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (1)
-Publisher SEC

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (3)
-Publisher SEC

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(4))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 7: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

+ Details

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

- Definition

Amount of increase in allowance for credit loss on financing receivable from recovery.

+ References

+ Details

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

- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

+ Details

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

- Definition

Amount of writeoff of financing receivable, charged against allowance for credit loss.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of credit loss expense (reversal of expense) for financing receivable.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04(11))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478524/942-220-S99-1

+ Details

Name:	us-gaap_ProvisionForLoanLossesExpensed
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=banr_MultifamilyRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=banr_ConstructionAndLandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=banr_CommercialBusinessAndSmallBusinessScoredMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=banr_AgriculturalBusinessMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=banr_OneToFourFamilyResidentialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=banr_CommercialBusinessMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: