FAIR VALUE MEASUREMENTS - Unobservable Inputs Non-recurring (Details) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2026 USD ($)	Dec. 31, 2025 USD ($)
FAIR VALUE MEASUREMENTS
Fair value asset level 1 to level 2	$ 0	$ 0
Fair value asset level 2 to level 1	0	0
Fair value liabilities level 1 to level 2	0	0
Fair value liabilities level 2 to level 1	0	0
Other real estate owned	7,146
Non-recurring \| Level 3
FAIR VALUE MEASUREMENTS
Individually evaluated loans, fair value	3,197	5,091
Other real estate owned	7,146
Premises held for sale	285	0
Total	10,628	5,091
Non-recurring \| Level 3 \| Commercial Real Estate Owner Occupied
FAIR VALUE MEASUREMENTS
Individually evaluated loans, fair value	352	378
Non-recurring \| Level 3 \| Commercial Real Estate Non-Owner Occupied
FAIR VALUE MEASUREMENTS
Individually evaluated loans, fair value	2,120	1,985
Non-recurring \| Level 3 \| Commercial and Industrial
FAIR VALUE MEASUREMENTS
Individually evaluated loans, fair value	565	2,410
Non-recurring \| Level 3 \| Residential Real Estate
FAIR VALUE MEASUREMENTS
Individually evaluated loans, fair value	$ 160	$ 318
Non-recurring \| Level 3 \| Impaired loans \| Residential Real Estate
FAIR VALUE MEASUREMENTS
Loss severity	35.00%	20.00%
Appraised value	$ 240	$ 240
Non-recurring \| Level 3 \| Other real estate owned
FAIR VALUE MEASUREMENTS
Appraised value	$ 8,600
Selling Costs	0.07
Non-recurring \| Level 3 \| Assets held for sale
FAIR VALUE MEASUREMENTS
Appraised value	$ 299
Selling Costs	0.05
Non-recurring \| Level 3 \| Minimum \| Impaired loans \| Commercial Real Estate Owner Occupied
FAIR VALUE MEASUREMENTS
Loss severity	43.00%	33.00%
Appraised value	$ 250	$ 250
Non-recurring \| Level 3 \| Minimum \| Impaired loans \| Commercial Real Estate Non-Owner Occupied
FAIR VALUE MEASUREMENTS
Loss severity	20.00%	20.00%
Appraised value	$ 466	$ 1,700
Non-recurring \| Level 3 \| Minimum \| Impaired loans \| Commercial and Industrial
FAIR VALUE MEASUREMENTS
Loss severity	15.00%	5.00%
Appraised value	$ 212	$ 212
Non-recurring \| Level 3 \| Maximum \| Impaired loans \| Commercial Real Estate Owner Occupied
FAIR VALUE MEASUREMENTS
Loss severity	70.00%	60.00%
Appraised value	$ 975	$ 975
Non-recurring \| Level 3 \| Maximum \| Impaired loans \| Commercial Real Estate Non-Owner Occupied
FAIR VALUE MEASUREMENTS
Loss severity	43.00%	40.00%
Appraised value	$ 1,775	$ 1,775
Non-recurring \| Level 3 \| Maximum \| Impaired loans \| Commercial and Industrial
FAIR VALUE MEASUREMENTS
Loss severity	80.00%	80.00%
Appraised value	$ 1,057	$ 1,112

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

No definition available.

Name:	bhb_FairValueAssetLevel1ToLevel2TransfersAmount
Namespace Prefix:	bhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

No definition available.

+ Details

Name:	bhb_FairValueAssetLevel2ToLevel1TransfersAmount
Namespace Prefix:	bhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the appraised value used as an input to measure fair value.

+ References

No definition available.

+ Details

Name:	bhb_FairValueInputsAppraisedValue
Namespace Prefix:	bhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of transfers of liabilities measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

+ References

No definition available.

+ Details

Name:	bhb_FairValueLiabilitiesLevel1ToLevel2TransferAmount
Namespace Prefix:	bhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of transfers of liabilities measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

+ References

No definition available.

+ Details

Name:	bhb_FairValueLiabilitiesLevel2ToLevel1TransferAmount
Namespace Prefix:	bhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of financing receivable individually evaluated for credit loss. Excludes financing receivable collectively evaluated for credit loss.

+ References

No definition available.

+ Details

Name:	bhb_FinancingReceivableIndividuallyEvaluatedForCreditLossFairValueDisclosure
Namespace Prefix:	bhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of other real estate owned.

+ References

No definition available.

+ Details

Name:	bhb_OtherRealEstateOwnedFairValueDisclosure
Namespace Prefix:	bhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of asset recognized for present right to economic benefit.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 100
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-100

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

+ Details

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

- Definition

Fair value portion of assets classified as held for sale.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 100
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-100

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-13

Reference 4: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 100
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-100

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

+ Details

Name:	us-gaap_AssetsHeldForSaleLongLivedFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 805
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 8
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479328/805-10-50-8

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 860
-SubTopic 50
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481229/860-50-50-2

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Topic 805
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 43
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479303/805-10-55-43

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(1)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 5: http://www.xbrl.org/2003/role/exampleRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 103
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482078/820-10-55-103

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)(i)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482106/820-10-50-2

+ Details

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

- Definition

Carrying amount of other real estate not separately disclosed, including, but not limited to, real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. This does not include real estate assets taken in settlement of troubled loans through surrender or foreclosure.

+ References

+ Details

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

- Definition

Value of input used to measure real estate owned by financial institution by financial institution which is not directly related to its business.

+ References

+ Details

Name:	us-gaap_OtherRealEstateOwnedMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of contractually collectible principal associated with a financial asset expected not to be collected due to default by the borrower.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 860
-SubTopic 50
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481229/860-50-50-2

+ Details

Name:	us-gaap_ServicingAssetsAndServicingLiabilitiesAtFairValueAssumptionsUsedToEstimateFairValueExpectedCreditLosses
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FairValueByAssetClassAxis=bhb_ImpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=us-gaap_RealEstateOtherMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=bhb_AssetsHeldForSaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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