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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

na

+ References

No definition available.

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- Definition

Amount of cost for defined contribution plan.

+ 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

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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

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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

+ References

No definition available.

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