Commitments and Contingent Liabilities - Contingencies (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2018
Overdraft fee litigation
Contingencies
Amount paid to settlement fund	$ 4.1
First Hawaiian Bank
Contingencies
Period for one-time continuous negative balance overdraft fee		7 days

Represents, for an overdrawn demand deposit account, the period the account remains in a negative balance after which a one-time continuous negative balance overdraft fee to be assessed.

No definition available.

Name:	fhb_OverdrawnDemandDepositAccountPeriodForOneTimeContinuousNegativeBalanceOverdraftFee
Namespace Prefix:	fhb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration