Transfers of Financial Assets - Carrying Amounts of Assets Pledged as Collateral, Borrowings and Other Transactions (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2019	Dec. 31, 2018
Carrying amounts of the assets pledged as collateral
Public deposits	$ 1,759,692	$ 1,749,726
Federal Home Loan Bank	2,589,411	2,497,030
Federal Reserve Bank	937,390	957,017
ACH transactions	152,579	150,903
Interest rate swaps	30,665	28,843
Total	5,469,737	5,383,519
Securities for reverse repurchase agreements	0	0
Extinguishment of debt
In-substance debt defeasance	$ 0	$ 0

Amount of debt extinguished by in-substance defeasance.

No definition available.

Name:	fhb_InSubstanceDebtDefeasanceAmount
Namespace Prefix:	fhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Sum of the carrying amounts as of the date of the latest financial statement presented of financial assets which are owned but transferred to another party to serve as collateral to partially or fully secure a debt obligation, repurchase agreement or other current or potential obligation, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

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

- Definition

The carrying amount as of the date of the latest financial statement presented of financial assets which are owned but transferred to serve as collateral for Automated Clearing House (ACH) obligations, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

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

- Definition

The carrying amount as of the date of the latest financial statement presented of financial assets which are owned but transferred to serve as collateral for derivative contracts, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

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

- Definition

The carrying amount, as of the date of the latest financial statement presented, of loans receivable and securities which are owned but transferred to serve as collateral for the payment of FHLB debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

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

- Definition

The carrying amount, as of the date of the latest financial statement presented, of loans receivable and securities which are owned but transferred to serve as collateral for the payment of Federal Reserve Bank debt obligations, and for which the transferee is not permitted to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

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

- Definition

The carrying amount as of the date of the latest financial statement presented of securities which are owned but transferred to serve as collateral for public deposits, and for which the transferee does not have the right by contract or custom to sell or re-pledge them to an unrelated party.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

The carrying value of securities purchased to be resold in reverse repurchase transactions as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(m)(2)(i))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

+ Details

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