Represents the funding swap agreement contingent conversion rate.

No definition available.

Name:	fhb_FundingSwapAgreementConversionRate
Namespace Prefix:	fhb_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Definition

The estimated payment paid to the buyer as a result of the reduction in the conversion rate.

+ References

No definition available.

+ Details

Name:	fhb_FundingSwapAgreementEstimatedPaymentToBuyer
Namespace Prefix:	fhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

The number of shares received by the entity from issuer in a stock transaction.

+ References

No definition available.

+ Details

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

- Definition

Cost to investors of each class of capital shares or other capital units.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-04.16(b)(1))
-URI http://asc.fasb.org/extlink&oid=120401414&loc=d3e603758-122996

+ Details

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

- Definition

Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in net income (trading).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(7)(c))
-URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227

+ Details

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

- Definition

Cost of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI). Excludes equity method investment and investment in equity security without readily determinable fair value.

+ References

No definition available.

+ Details

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

- Definition

Balance held at close of period in number of shares.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 210
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=99383244&loc=d3e12121-115841

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 946
-SubTopic 320
-Section S99
-Paragraph 3
-Subparagraph (SX 210.12-12B(Column B))
-URI http://asc.fasb.org/extlink&oid=120401592&loc=d3e611197-123010

+ Details

Name:	us-gaap_InvestmentOwnedBalanceShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
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_ScheduleOfTradingSecuritiesAndOtherTradingAssetsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=fhb_VisaIncorporatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	fhb_InvestmentSecuritiesIssuerAxis=fhb_VisaIncorporatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Investment Securities - Visa Class B Restricted Shares (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016 USD ($) shares	Dec. 31, 2008 USD ($) shares	Jun. 30, 2021 USD ($) shares	Dec. 31, 2020 USD ($) shares	Oct. 31, 2019 USD ($)	Sep. 30, 2019	Sep. 27, 2019	Jul. 31, 2018 USD ($)	Jul. 05, 2018	Jun. 28, 2018	Dec. 31, 2017
Visa \| Class B restricted shares
Visa Class B Restricted Shares
Historical cost included in the balance sheets		$ 0
Net realized gain related to the sale of stock	$ 22,700
Number of shares sold \| shares	274,000
Estimated amount that was subsequently paid to the buyer					$ 300
Shares held \| shares			120,000	120,000
Cost basis			$ 0	$ 0
Visa Derivative \| Class B restricted shares
Visa Class B Restricted Shares
Conversion rate						1.6228	1.6228		1.6298	1.6298	1.6483
Visa Derivative \| Visa
Visa Class B Restricted Shares
Estimated amount that was subsequently paid to the buyer					$ 300			$ 700
Visa \| Class B restricted shares
Visa Class B Restricted Shares
Stock received in initial public offering (in shares) \| shares		394,000