Note 5 - Qualified Affordable Housing Partnership Investments - Original Investment in LIHTC Projects (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Original Investment	$ 7,954		$ 7,954
Current Recorded Investment	3,391		3,529
Unfunded Liability Obligation	330		361
Tax Credits and Benefits	146	$ 203
Amortization of Investments	138	171
Net Income Tax Benefit	8	32
Raymond James California Housing Opportunities Fund II [Member]
Original Investment	2,000		2,000
Current Recorded Investment	1,138		1,182
Unfunded Liability Obligation	15		20
Tax Credits and Benefits	50	56
Amortization of Investments	44	45
Net Income Tax Benefit	6	11
WNC Institutional Tax Credit Fun 38 L.P. [Member]
Original Investment	1,000		1,000
Current Recorded Investment	563		589
Unfunded Liability Obligation
Tax Credits and Benefits	32	35
Amortization of Investments	26	26
Net Income Tax Benefit	6	9
Merritt Community Capital Corporation Fund XV, L.P. [Member]
Original Investment	2,500		2,500
Current Recorded Investment	1,420		1,476
Unfunded Liability Obligation	315		341
Tax Credits and Benefits	56	68
Amortization of Investments	56	56
Net Income Tax Benefit		12
California Affordable Housing Fund [Member]
Original Investment	2,454		2,454
Current Recorded Investment	270		282
Unfunded Liability Obligation
Tax Credits and Benefits	8	44
Amortization of Investments	12	44
Net Income Tax Benefit	$ (4)

The total amount of affordable housing tax credits and tax benefit from operating losses recognized.

No definition available.

Name:	boch_AffordableHousingTaxCreditsAndBenefitsAmount
Namespace Prefix:	boch_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of investments in qualified affordable housing projects using proportional amortization method.

No definition available.

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

Amount of amortization of investments in qualified affordable housing projects using proportional amortization method.

No definition available.

Name:	boch_ProportionalAmortizationMethodQualifiedAffordableHousingProjectInvestmentsAmortization
Namespace Prefix:	boch_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The net income tax benefit amount of investments in qualified affordable housing projects using proportional amortization method.

No definition available.

Name:	boch_ProportionalAmortizationMethodQualifiedAffordableHousingProjectInvestmentsNetIncomeTaxBenefit
Namespace Prefix:	boch_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

The original amount of investments in qualified affordable housing projects using proportional amortization method.

No definition available.

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

The unfunded liability obligation amount of investments in qualified affordable housing projects using proportional amortization method.

No definition available.

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

Name:	us-gaap_InvestmentTypeAxis=boch_RaymondJamesCaliforniaHousingOpportunitiesFundIIMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_InvestmentTypeAxis=boch_WNCInstitutionalTaxCreditFun38LPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_InvestmentTypeAxis=boch_MerrittCommunityCapitalCorporationFundXVLPMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_InvestmentTypeAxis=boch_CaliforniaAffordableHousingFundMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: