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Commitments and Contingent Liabilities - Contingencies (Details) | 6 Months Ended
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Jun. 30, 2018 USD ($)
Overdraft fee litigation |
Contingencies |
Loss contingency liability | $ 0
First Hawaiian Bank |
Contingencies |
Period for one-time continuous negative balance overdraft fee | 7 days

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- Definition Represents, for an overdrawn demand deposit account, the period the account remains in a negative balance after which a one-time continuous negative balance overdraft fee to be assessed. + References No definition available. + Details
Name: | fhb_OverdrawnDemandDepositAccountPeriodForOneTimeContinuousNegativeBalanceOverdraftFee
Namespace Prefix: | fhb_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- 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_LossContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of loss contingency liability. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349 + Details
Name: | us-gaap_LossContingencyAccrualAtCarryingValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_LitigationCaseAxis=fhb_OverdraftFeeLitigationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | dei_LegalEntityAxis=fhb_FirstHawaiianBankMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |