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Benefit Plans - 401(k) Savings Plan (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Salaries and employee benefits |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer contributions | $ 10.1 | $ 9.3 | $ 9.2
Savings Plan and Money Purchase Pension Plan [Abstract] |  |  |
Employer contributions | $ 10.1 | $ 9.3 | $ 9.2
First Hawaiian, Inc. 401(k) Savings Plan | Maximum [Member] |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer contributions, as percentage of employee's pay | 5.00% | 5.00% | 5.00%
Savings Plan and Money Purchase Pension Plan [Abstract] |  |  |
Employer contributions, as percentage of employee's pay | 5.00% | 5.00% | 5.00%
First Hawaiian, Inc. Future Plan |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer contributions, as percentage of employee's pay | 2.50% | 2.50% | 2.50%
Savings Plan and Money Purchase Pension Plan [Abstract] |  |  |
Employer contributions, as percentage of employee's pay | 2.50% | 2.50% | 2.50%

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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 Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480794/715-70-50-1 + Details
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