Note 9 - Fair Values (Details Textual) $ in Thousands	9 Months Ended
Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Collateral Dependent Impaired Loans [Member]
Collateral Dependent Impaired Loans Carrying Amount	$ 4,300	$ 10,500
Collateral Dependent Impaired Loans, Fair Value Disclosure	3,800	10,200
Allowance for Loan and Lease Losses, Adjustments, Other	498	328
Collateral Impaired Loans [Member]
Collateral Dependent Impaired Loans Carrying Amount	14	101
Collateral Dependent Impaired Loans, Fair Value Disclosure	8	58
Allowance for Loan and Lease Losses, Adjustments, Other	$ 6	$ 43
Number of Real Estate Properties	1	2
Measurement Input, Cost to Sell [Member]
Other Real Estate Owned, Measurement Input	0.52
Measurement Input, Cost to Sell [Member] \| Collateral Dependent Impaired Loans [Member] \| Minimum [Member]
Loans Held-for-sale, Measurement Input	0.08
Measurement Input, Cost to Sell [Member] \| Collateral Dependent Impaired Loans [Member] \| Maximum [Member]
Loans Held-for-sale, Measurement Input	0.10

The carrying amount on collateral dependent impaired loans.

No definition available.

Name:	boch_CollateralDependentImpairedLoansCarryingAmount
Namespace Prefix:	boch_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the fair value portion of collateral dependent impaired loans.

+ References

No definition available.

+ Details

Name:	boch_CollateralDependentImpairedLoansFairValueDisclosure
Namespace Prefix:	boch_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of other addition (reduction) in allowance reserve for credit loss.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesAdjustmentsNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Value of input used to measure loan, held for sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfRealEstateProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Value of input used to measure real estate owned by financial institution by financial institution which is not directly related to its business.

+ References

+ Details

Name:	us-gaap_OtherRealEstateOwnedMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputCostToSellMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=boch_CollateralDependentImpairedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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