Allowance for Credit Losses - Amortized Cost Basis of Loans and Leases on Nonaccrual Status (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans and Leases With No Allowance for Credit Losses	$ 2,890		$ 1,919
Nonaccrual Loans and Leases	8,601		7,082
Interest income recognized on nonaccrual loans and leases	0	$ 100
Accrued interest receivables written off, Interest income reversed	200	$ 400
Commercial and Industrial
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans and Leases	707		718
Commercial real estate
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans and Leases With No Allowance for Credit Losses	727		727
Nonaccrual Loans and Leases	727		727
Lease financing
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans and Leases	75
Residential. Mortgage
Financing Receivable, Nonaccrual [Line Items]
Nonaccrual Loans and Leases With No Allowance for Credit Losses	2,163		1,192
Nonaccrual Loans and Leases	$ 7,092		$ 5,637

Represents the interest receivable written off by reversing interest income.

No definition available.

Name:	fhb_LoanAndLeaseLossesWriteOffsReversalOfInterestIncome
Namespace Prefix:	fhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of financing receivable on nonaccrual status with no allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447

+ Details

Name:	us-gaap_FinancingReceivableNonaccrualNoAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_FinancingReceivableNonaccrualStatusLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of financing receivable on nonaccrual status.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5111-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 16
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919258-210447

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (3)

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (2)

+ Details

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

- Definition

The amount of interest income on impaired and nonperforming loans that is due to the change in present value attributable to the passage of time.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 19
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5278-111524

+ Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_FinanceLeasesPortfolioSegmentMember
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: