Note 5 - Loans (Details Textual) $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Unamortized Loan Commitment and Origination Fees and Unamortized Discounts or Premiums, Total	$ 2,500	$ 2,800
Loans and Leases Receivable, Impaired, Interest Lost on Nonaccrual Loans	166	226	$ 353
Impaired Financing Receivable, Recorded Investment, Total	$ 11,012	$ 13,147
Percentage of Collateral Coverage to Loan Balance to Consider Restructured Loan to Performing and Accrual Status	100.00%
Financing Receivable, Modifications, Number of Contracts	0	1	8
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 4,146	$ 5,799
Financing Receivable, Modifications, Recorded Investment	$ 9,600	$ 10,900
Financing Receivable, Number of Contracts Qualified as Troubled Debt Restructuring	106
Troubled Debt Restructurings Percentage of Gross Portfolio Loans	1.01%	1.24%
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0	0	0
Doubtful Grade Remaining Outstanding Period, Minimum	180 days
Mortgage Loans in Process of Foreclosure, Amount	$ 245
Loans and Leases Receivable, Allowance, Ending Balance	$ 12,292	$ 11,925
Percentage of Allowance for Loan and Lease Losses out of Net Loans	1.30%	1.36%
Fair Value Disclosure, Off-balance Sheet Risks, Amount, Asset	$ 235,800	$ 227,700
Reserve for Unfunded Commitments Included in Other Liabilities	$ 695	$ 695
Percentage of Loan Portfolio Secured by Real Estate	81.00%
Percentage of Unallocated Allowance Amount out of Allowance for Loan and Lease Losses	4.00%	3.00%
Maximum Loan to Value, Percentage	80.00%
Commercial Portfolio Segment [Member]
Impaired Financing Receivable, Recorded Investment, Total	$ 2,183	$ 3,154
Financing Receivable, Modifications, Number of Contracts			4
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 959	$ 1,603
Commercial Portfolio Segment [Member] \| Line of Credit [Member]
Financing Receivable, Modifications, Number of Contracts	1	1
Financing Receivable, Recorded Investment, Nonaccrual Status	$ 313	$ 33
Performing Financial Instruments [Member]
Impaired Financing Receivable, Recorded Investment, Total	6,900	7,300
Federal Home Loan Bank of San Francisco [Member]
Loans Pledged as Collateral	$ 436,100	$ 420,000

Period that a loan classified as Doubtful will remain outstanding.

No definition available.

Name:	boch_DoubtfulGradeRemainingOutstandingPeriodMinimum
Namespace Prefix:	boch_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of financing receivables that qualified as troubled debt restructurings.

+ References

No definition available.

+ Details

Name:	boch_FinancingReceivableNumberOfContractsQualifiedAsTroubledDebtRestructuring
Namespace Prefix:	boch_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The maximum loan to value percentage.

+ References

No definition available.

+ Details

Name:	boch_MaximumLoanToValuePercentage
Namespace Prefix:	boch_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of the allowance for loan and lease losses as a percentage of total gross loans.

+ References

No definition available.

+ Details

Name:	boch_PercentageOfAllowanceForLoanAndLeaseLossesOutOfNetLoans
Namespace Prefix:	boch_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of collateral coverage to loan balance, to consider restructured loan to performing and accrual status.

+ References

No definition available.

+ Details

Name:	boch_PercentageOfCollateralCoverageToLoanBalanceToConsiderRestructuredLoanToPerformingAndAccrualStatus
Namespace Prefix:	boch_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of the gross loan portfolio that is secured by real estate.

+ References

No definition available.

+ Details

Name:	boch_PercentageOfLoanPortfolioSecuredByRealEstate
Namespace Prefix:	boch_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of unallocated allowance amount out of allowance for loan and lease losses.

+ References

No definition available.

+ Details

Name:	boch_PercentageOfUnallocatedAllowanceAmountOutOfAllowanceForLoanAndLeaseLosses
Namespace Prefix:	boch_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the reserve for unfunded commitments.

+ References

No definition available.

+ Details

Name:	boch_ReserveForUnfundedCommitmentsIncludedInOtherLiabilities
Namespace Prefix:	boch_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage of gross portfolio loans that are classified as loans modified under a troubled debt restructuring.

+ References

No definition available.

+ Details

Name:	boch_TroubledDebtRestructuringsPercentageOfGrossPortfolioLoans
Namespace Prefix:	boch_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The fair value of financial assets, which are not recognized in the financial statements (off-balance sheet) because they fail to meet some other criterion for recognition.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13433-108611

+ Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsNumberOfContracts2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18845-111554

+ Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultNumberOfContracts1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

+ Details

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

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953550-111524

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=82894903&loc=d3e15032-111544

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

+ Details

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

- Definition

Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18794-111554

+ Details

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

- Definition

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5086-111524

+ Details

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

- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL49126937-111524

+ Details

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

- Definition

Amount of deferred fees paid by borrowers and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield. Excludes amounts for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancialInstrumentPerformanceStatusAxis=us-gaap_PerformingFinancingReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis=srt_FederalHomeLoanBankOfSanFranciscoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: