Investment Securities - Amortized Cost and Fair Value of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Available for sale debt securities
Amortized Cost	$ 5,357,275	$ 5,176,615
Unrealized Gains	241	1,984
Unrealized Losses	(122,858)	(101,085)
Fair value	5,234,658	5,077,514
U.S. Treasury securities
Available for sale debt securities
Amortized Cost	404,376	405,637
Unrealized Losses	(12,121)	(13,164)
Fair value	392,255	392,473
Government-sponsored enterprises debt securities
Available for sale debt securities
Amortized Cost	249,712	249,707
Unrealized Gains		16
Unrealized Losses	(7,111)	(7,056)
Fair value	242,601	242,667
Government agency mortgage-backed securities
Available for sale debt securities
Amortized Cost	356,858	190,485
Unrealized Losses	(5,468)	(4,822)
Fair value	351,390	185,663
Government-sponsored enterprises mortgage-backed securities
Available for sale debt securities
Amortized Cost	178,702	208,034
Unrealized Gains	169	385
Unrealized Losses	(4,130)	(4,034)
Fair value	174,741	204,385
Non-government asset-backed securities
Available for sale debt securities
Amortized Cost		12,592
Unrealized Losses		(9)
Fair value		12,583
Collateralized mortgage obligations: Government agency
Available for sale debt securities
Amortized Cost	3,367,173	3,409,822
Unrealized Gains	47	794
Unrealized Losses	(76,746)	(58,794)
Fair value	3,290,474	3,351,822
Collateralized mortgage obligations: Government-sponsored enterprises
Available for sale debt securities
Amortized Cost	779,911	700,338
Unrealized Gains	25	789
Unrealized Losses	(17,218)	(13,206)
Fair value	762,718	$ 687,921
States and political subdivisions
Available for sale debt securities
Amortized Cost	20,543
Unrealized Losses	(64)
Fair value	$ 20,479

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt securities classified as available-for-sale.

+ References

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- References

No definition available.

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of debt securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27161-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 320
-Section 50
-Paragraph 2
-Subparagraph (b)-(g)
-URI http://asc.fasb.org/extlink&oid=75019621&loc=d3e62557-112803

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=fhb_MortgageBackedSecuritiesIssuedByUsGovernmentAgenciesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_AssetBackedSecuritiesSecuritizedLoansAndReceivablesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=fhb_CollateralizedMortgageObligationsIssuedByUsGovernmentAgenciesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=fhb_CollateralizedMortgageObligationsIssuedByUsGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtSecurityAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: