Investment Securities - Other-Than-Temporary Impairment (Details) - USD ($)	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Investment Securities
Other than temporary impairment recognized	$ 0	$ 0

Amount of other-than-temporary impairment (OTTI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), recognized in earnings and other comprehensive loss (OCI).

No definition available.

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