Leases - Lease Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows paid for operating leases	$ 8,848	$ 8,802
Operating cash flows paid for finance leases		10
Financing cash flows paid for finance leases	10	10
Right-of-use assets obtained in exchange for new lease obligations, Operating leases	$ 3,796	$ 1,401
Weighted Average Remaining Lease Term, Operating leases (years)	16 years 1 month 6 days	15 years 8 months 12 days
Weighted Average Remaining Lease Term, Finance leases (years)	1 year 6 months	2 years 6 months
Weighted Average Discount Rate, Operating leases	3.17%	3.36%
Weighted Average Discount Rate, Finance leases	6.78%	6.78%
Operating lease right-of-use assets	$ 40,200	$ 44,300
Other assets	us-gaap:OtherAssetsMember	us-gaap:OtherAssetsMember
Operating lease liabilities	$ 40,600	$ 44,400
Other liabilities	us-gaap:OtherLiabilitiesMember	us-gaap:OtherLiabilitiesMember
Finance lease right-of use assets	$ 0	$ 0
Premises and equipment	fhb:PremisesAndEquipmentMember	fhb:PremisesAndEquipmentMember
Finance lease liabilities	$ 10	$ 19
Long-term borrowings	us-gaap:LongTermDebtMember	us-gaap:LongTermDebtMember