Allowance for Credit Losses - Updated Methodology for Estimate of Total ACL (Details) $ in Millions	6 Months Ended
Jun. 30, 2024 USD ($)
Allowance for Credit Losses
Net decrease in ACL due to updates in models	$ 3.2
Updated certain components resulting in increase to the Total ACL	5.8
Total decrease to ACL from change in method	$ (9.0)

Amount of credit loss expense (reversal of expense) on financing receivable and net investment in lease from change in certain components.

No definition available.

Name:	fhb_FinancingReceivableAndNetInvestmentInLeaseChangeInCertainComponentsCreditLossExpenseReversal
Namespace Prefix:	fhb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration