Represents the number of interest rate swaps held by the entity at the reporting date.

No definition available.

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Cap rate on an interest rate derivative such as an interest rate cap or collar. If market rates exceed the cap rate, a payment or receipt is triggered on the contract.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeCapInterestRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Fixed interest rate related to the interest rate derivative.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFixedInterestRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Floor rate on an interest rate derivative such as an interest rate floor or collar. If market rates falls below the floor rate, a payment or receipt is triggered on the contract.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeFloorInterestRate
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Estimated period for the anticipated transfer of gain (loss), net, from accumulated other comprehensive income into earnings, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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

- Definition

The estimated value of gains (losses), net anticipated to be transferred in the future from accumulated other comprehensive income into earnings.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480870/815-30-50-1

+ Details

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

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 815
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 181
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480401/815-10-55-181

Reference 2: 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 3: 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

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Fair value as of the balance sheet date of interest rate derivative assets, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as assets.

+ References

No definition available.

+ Details

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

- Definition

Fair value as of the balance sheet date of interest rate derivative liabilities, which includes all such derivative instruments in hedging and nonhedging relationships that are recognized as liabilities.

+ References

No definition available.

+ Details

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

- Definition

Number of interest rate derivative instruments held by the entity at the reporting date.

+ References

Reference 1: 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 2: 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

+ Details

Name:	us-gaap_NumberOfInterestRateDerivativesHeld
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_OtherComprehensiveIncomeLocationAxis=us-gaap_OtherComprehensiveIncomeMember
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_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentsGainLossByHedgingRelationshipAxis=us-gaap_FairValueHedgingMember
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:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
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- Details

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

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateFloorMember
Namespace Prefix:
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Derivative Financial Instruments - Fair Value Hedges and Cash Flow Hedges (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2025 USD ($) derivative	Dec. 31, 2024 USD ($) derivative	Sep. 30, 2024 USD ($) derivative
Other Comprehensive Income (Loss)
Fair hedges carried
Accumulated other comprehensive income (loss) into earnings	$ 1,000
Hedge term	3 years
Designated as hedging instruments \| Interest rate derivatives
Fair hedges carried
Notional amounts	$ 60,938	$ 63,750
Designated as hedging instruments \| Interest rate derivatives \| Fair Value Hedging
Fair hedges carried
Number of interest rate swaps \| derivative	1	1
Notional amounts	$ 60,900	$ 63,800
Positive fair value	$ 8,000	8,800
Fixed interest rates (as a percent)	2.07%
Designated as hedging instruments \| Interest rate derivatives \| Cash Flow Hedging
Fair hedges carried
Number of derivatives carried \| derivative			2
Notional amounts			$ 200,000
Designated as hedging instruments \| Interest rate derivatives \| Cash Flow Hedging \| Minimum
Fair hedges carried
Fixed interest rates (as a percent)			1.70%
Designated as hedging instruments \| Interest rate derivatives \| Cash Flow Hedging \| Maximum
Fair hedges carried
Fixed interest rates (as a percent)			2.08%
Designated as hedging instruments \| Interest rate collars
Fair hedges carried
Notional amounts	$ 100,000	$ 200,000
Designated as hedging instruments \| Interest rate collars \| Cash Flow Hedging
Fair hedges carried
Number of derivatives carried \| derivative	1	2
Notional amounts	$ 100,000	$ 200,000
Positive fair value	$ 100
Negative fair value		$ 100
Floor strike rate	2.00%	2.00%
Cap strike rates	5.64%
Designated as hedging instruments \| Interest rate collars \| Cash Flow Hedging \| Minimum
Fair hedges carried
Cap strike rates		5.31%
Designated as hedging instruments \| Interest rate collars \| Cash Flow Hedging \| Maximum
Fair hedges carried
Cap strike rates		5.64%
Designated as hedging instruments \| Interest rate floors
Fair hedges carried
Notional amounts	$ 300,000
Designated as hedging instruments \| Interest rate floors \| Cash Flow Hedging
Fair hedges carried
Number of derivatives carried \| derivative	3
Notional amounts	$ 300,000
Positive fair value	$ 2,300
Designated as hedging instruments \| Interest rate floors \| Cash Flow Hedging \| Minimum
Fair hedges carried
Floor strike rate	2.95%
Designated as hedging instruments \| Interest rate floors \| Cash Flow Hedging \| Maximum
Fair hedges carried
Floor strike rate	3.00%