Organization and Summary of Significant Accounting Policies - Allowance for Credit Losses (Details)	12 Months Ended
Dec. 31, 2020 segment
Organization and Summary of Significant Accounting Policies
Estimated credit loss model, forecast horizon	1 year
Number of portfolio segments	3

Represents the forecast horizon period in regards to the estimated credit loss model.

No definition available.

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