Investment Securities (Amortization Cost, Gross Unrealized Gains/Losses, and Fair Value) (Details 1) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Available-for-Sale:
Available-for-Sale: Amortized Cost	$ 2,637,898	$ 2,022,158
Available-for-Sale: Gross Unrealized Gains	22,546	9,225
Available-for-Sale: Gross Unrealized Losses	(10,495)	(23,441)
Available-for-Sale	2,649,949	2,007,942
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	2,959,611	3,482,092
Held-to-Maturity: Gross Unrealized Gains	27,211	11,959
Held-to-Maturity: Gross Unrealized Losses	(13,593)	(80,057)
Held-to-Maturity: Fair Value	2,973,229	3,413,994
Debt Securities Issued by Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	192	56
Available-for-Sale: Gross Unrealized Gains	4	0
Available-for-Sale: Gross Unrealized Losses	0	0
Available-for-Sale	196
Residential - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	1,219,120	189,645
Available-for-Sale: Gross Unrealized Gains	12,519	1,726
Available-for-Sale: Gross Unrealized Losses	(3,709)	(929)
Available-for-Sale	1,227,930	190,442
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	1,219,447	1,861,874
Held-to-Maturity: Gross Unrealized Gains	13,744	3,886
Held-to-Maturity: Gross Unrealized Losses	(8,002)	(51,773)
Held-to-Maturity: Fair Value	1,225,189	1,813,987
Residential - U.S. Government-Sponsored Enterprises
Available-for-Sale:
Available-for-Sale: Amortized Cost	500,664	589,311
Available-for-Sale: Gross Unrealized Gains	4,663	1,779
Available-for-Sale: Gross Unrealized Losses	(2,270)	(12,563)
Available-for-Sale	503,057	578,527
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	1,218,431	758,835
Held-to-Maturity: Gross Unrealized Gains	10,095	1,590
Held-to-Maturity: Gross Unrealized Losses	(3,232)	(20,259)
Held-to-Maturity: Fair Value	1,225,294	740,166
Commercial - Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	170,567	63,864
Available-for-Sale: Gross Unrealized Gains	2,960	0
Available-for-Sale: Gross Unrealized Losses	(2,324)	(4,484)
Available-for-Sale	171,203	59,380
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	86,162	176,393
Held-to-Maturity: Gross Unrealized Gains	215	147
Held-to-Maturity: Gross Unrealized Losses	(1,863)	(5,177)
Held-to-Maturity: Fair Value	84,514	171,363
Mortgage-Backed Securities
Available-for-Sale:
Available-for-Sale: Amortized Cost	1,890,351	842,820
Available-for-Sale: Gross Unrealized Gains	20,142	3,505
Available-for-Sale: Gross Unrealized Losses	(8,303)	(17,976)
Available-for-Sale	1,902,190	828,349
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	2,524,040	2,797,102
Held-to-Maturity: Gross Unrealized Gains	24,054	5,623
Held-to-Maturity: Gross Unrealized Losses	(13,097)	(77,209)
Held-to-Maturity: Fair Value	2,534,997	2,725,516
Debt Securities Issued by the U.S. Treasury and Government Agencies
Available-for-Sale:
Available-for-Sale: Amortized Cost	336,474	394,485
Available-for-Sale: Gross Unrealized Gains	496	493
Available-for-Sale: Gross Unrealized Losses	(1,438)	(2,577)
Available-for-Sale	335,532	392,401
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	353,721	353,122
Held-to-Maturity: Gross Unrealized Gains	1,752	186
Held-to-Maturity: Gross Unrealized Losses	(262)	(1,093)
Held-to-Maturity: Fair Value	355,211	352,215
Debt Securities Issued by States and Political Subdivisions
Available-for-Sale:
Available-for-Sale: Amortized Cost	61,228	559,800
Available-for-Sale: Gross Unrealized Gains	993	5,227
Available-for-Sale: Gross Unrealized Losses	(2)	(1,031)
Available-for-Sale	62,219	563,996
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	65,421	234,602
Held-to-Maturity: Gross Unrealized Gains	1,405	6,150
Held-to-Maturity: Gross Unrealized Losses	0	0
Held-to-Maturity: Fair Value	66,826	240,752
Debt Securities Issued by Corporations
Available-for-Sale:
Available-for-Sale: Amortized Cost	349,653	224,997
Available-for-Sale: Gross Unrealized Gains	911	0
Available-for-Sale: Gross Unrealized Losses	(752)	(1,857)
Available-for-Sale	349,812	223,140
Debt Securities, Held-to-maturity, Fair Value to Amortized Cost [Abstract]
Held-to-Maturity: Amortized Cost	16,429	97,266
Held-to-Maturity: Gross Unrealized Gains	0	0
Held-to-Maturity: Gross Unrealized Losses	(234)	(1,755)
Held-to-Maturity: Fair Value	$ 16,195	$ 95,511

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

No definition available.

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

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
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 and equity securities classified as available-for-sale.

+ References

No definition available.

+ Details

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

- Definition

This item represents the cost of debt and equity 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

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

+ Details

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

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

+ Details

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

- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

+ Details

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

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=boh_ResidentialMortgageBackedSecuritiesIssuedByUSGovernmentAgenciesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=boh_ResidentialMortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=boh_CommercialMortgageBackedSecuritiesIssuedByGovernmentAgenciesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=boh_DebtSecuritiesIssuedByUnitedStatesTreasuryAndGovernmentAgenciesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: