DERIVATIVE FINANCIAL INSTRUMENTS AND HEDGING ACTIVITIES - Derivative Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 265,453		$ 182,239
Estimated Fair Value Asset (Liability)	(256)		811
Designated as hedging instrument \| Cash flow hedges:
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	140,000		$ 90,000
Weighted Average Maturity (in years)			4 years 1 month 6 days
Estimated Fair Value Asset (Liability)	(205)		$ 803
Designated as hedging instrument \| Cash flow hedges: \| Interest rate cap agreements
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 90,000		$ 90,000
Weighted Average Maturity (in years)	3 years 10 months 24 days		4 years 1 month 6 days
Estimated Fair Value Asset (Liability)	$ 320		$ 803
Realized gains (losses)	163	$ (108)
Designated as hedging instrument \| Cash flow hedges: \| Interest Rate Swap
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 50,000
Weighted Average Maturity (in years)	5 years
Estimated Fair Value Asset (Liability)	$ (525)
Designated as hedging instrument \| Economic hedges:
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	3,257
Estimated Fair Value Asset (Liability)	(65)
Designated as hedging instrument \| Economic hedges: \| Forward sale commitments
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 3,257
Weighted Average Maturity (in years)	1 month 6 days
Estimated Fair Value Asset (Liability)	$ (65)
Realized gains (losses)	(65)	170
Not designated as hedging instrument
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	122,196		92,239
Estimated Fair Value Asset (Liability)	14		8
Not designated as hedging instrument \| Interest rate lock commitments
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 4,828		$ 957
Weighted Average Maturity (in years)	1 month 6 days		1 month 6 days
Estimated Fair Value Asset (Liability)	$ 14		$ 8
Realized gains (losses)	6	$ 8
Not designated as hedging instrument \| Customer loan derivative liability
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 58,684		$ 45,641
Weighted Average Maturity (in years)	10 years 9 months 18 days		9 years 10 months 24 days
Estimated Fair Value Asset (Liability)	$ (2,852)		$ (1,353)
Not designated as hedging instrument \| Customer loan derivative asset
Interest rate swap agreements and non-hedging derivative assets and liabilities
Notional Amount	$ 58,684		$ 45,641
Weighted Average Maturity (in years)	10 years 9 months 18 days		9 years 10 months 24 days
Estimated Fair Value Asset (Liability)	$ 2,852		$ 1,353

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair values as of the balance sheet date of the net amount of all assets and liabilities resulting from contracts that meet the criteria of being accounted for as derivative instruments.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=6945355&loc=d3e41228-113958

+ Details

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

- Definition

Average remaining period until maturity of the derivative contract, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeAverageRemainingMaturity1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

The difference between the book value and the sale price of options, swaps, futures, forward contracts, and other derivative instruments. This element refers to the gain (loss) included in earnings.

+ References

Reference 1: 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=109223946&loc=d3e3602-108585

Reference 2: 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(h))
-URI http://asc.fasb.org/extlink&oid=114873765&loc=SL114874048-224260

+ Details

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

- 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_InterestRateCapMember
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_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=bhb_EconomicHedgingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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