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Organization and Basis of Presentation - Subsidiary Ownership (Details) | Jun. 30, 2018
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First Hawaiian Bank |
Capitalization |
Outstanding common stock owned (as a percent) | 100.00%

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- Definition The parent entity's interest in net assets of the subsidiary, expressed as a percentage. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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

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