Benefit Plans - 401(k) Savings Plan (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Salaries and employee benefits
Defined Contribution Plan Disclosure [Line Items]
Employer contributions	$ 9.2	$ 9.1	$ 8.6
First Hawaiian, Inc. 401(k) Savings Plan | Maximum
Defined Contribution Plan Disclosure [Line Items]
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%