Name:	fhb_ForeignBankingOrganizationsUnitedStatesIntermediateHoldingCompanyRequirementUnitedStatesNonBranchAssetsThreshold
Namespace Prefix:	fhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The number of shares of an investment sold during the period.

No definition available.

Name:	fhb_InvestmentOwnedSharesSold
Namespace Prefix:	fhb_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Percentage of subsidiary's or equity investee's stock owned by parent company sold in stock transaction.

No definition available.

Name:	fhb_SaleOfStockPercentageOfOwnershipSoldInTransaction
Namespace Prefix:	fhb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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

No definition available.

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Percentage of subsidiary's or equity investee's stock owned by parent company after stock transaction.

No definition available.

Name:	us-gaap_SaleOfStockPercentageOfOwnershipAfterTransaction
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of subsidiary's or equity investee's stock owned by parent company before stock transaction.

No definition available.

Name:	us-gaap_SaleOfStockPercentageOfOwnershipBeforeTransaction
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Price of a single share of a number of saleable stocks of a company.

No definition available.

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant

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.

No definition available.

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

Name:	dei_LegalEntityAxis=fhb_BnpParibasMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_OwnershipAxis=fhb_FirstHawaiianIncorporatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubsidiarySaleOfStockAxis=us-gaap_IPOMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubsidiarySaleOfStockAxis=fhb_SecondaryOfferingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubsidiarySaleOfStockAxis=us-gaap_OverAllotmentOptionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_StatementScenarioAxis=us-gaap_PredecessorMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_SubsidiarySaleOfStockAxis=fhb_ReorganizationTransactionsApril2016Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_OwnershipAxis=fhb_BankOfWestMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: