Organization and Basis of Presentation (Details)	9 Months Ended
Sep. 30, 2023 item
Capitalization
Loan modification, period of nonaccrual status	6 months
Estimated credit loss model, forecast horizon	1 year
Number of Portfolio Segments	3
Commercial Lending
Capitalization
Number of distinct classes within portfolio segment	4
Residential mortgage
Capitalization
Number of distinct classes within portfolio segment	2
First Hawaiian, Inc. (FHI)
Capitalization
Outstanding common stock owned (as a percent)	100.00%

Represents the forecast horizon period in regards to the estimated credit loss model.

No definition available.

Name:	fhb_EstimatedCreditLossForecastHorizon
Namespace Prefix:	fhb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the minimum period of time that modified loans remain on nonaccrual status.

+ References

No definition available.

+ Details

Name:	fhb_FinancingReceivableModificationsMinimumPeriodOnNonaccrualStatus
Namespace Prefix:	fhb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of distinct classes of loans within particular portfolio segments.

+ References

No definition available.

+ Details

Name:	fhb_NumberOfClassesOfLoansWithinParticularPortfolioSegment
Namespace Prefix:	fhb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of portfolio segments.

+ References

No definition available.

+ Details

Name:	fhb_NumberOfPortfolioSegments
Namespace Prefix:	fhb_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
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_ScheduleOfCapitalizationEquityLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=fhb_FirstHawaiianIncorporatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: