Note 5 - Loans - Allowance for Credit Losses and Recorded Investment in Financing Receivables (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Dec. 31, 2016
Balance	$ 11,544	$ 11,180
Charge-offs	(447)	(307)
Recoveries	344	622
Provision	200
Balance	11,641	11,495
Individually evaluated for impairment			$ 1,274	$ 1,461
Collectively evaluated for impairment			10,367	10,083
Total	11,544	11,180	11,641	11,544
Individually evaluated for impairment			16,757	18,794
Collectively evaluated for impairment			793,437	785,417
Total gross loans			810,194	804,211
Commercial Portfolio Segment [Member]
Balance	2,849	2,493
Charge-offs	(51)	(85)
Recoveries	199	32
Provision	(348)	26
Balance	2,649	2,466
Individually evaluated for impairment			491	641
Collectively evaluated for impairment			2,158	2,208
Total	2,849	2,493	2,649	2,849
Individually evaluated for impairment			3,275	3,525
Collectively evaluated for impairment			142,360	150,319
Total gross loans			145,635	153,844
Commercial Real Estate Portfolio Segment [Member]
Balance	5,578	5,784
Charge-offs		(6)
Recoveries	27	528
Provision	358	(414)
Balance	5,963	5,892
Individually evaluated for impairment			142	85
Collectively evaluated for impairment			5,821	5,493
Total	5,578	5,784	5,963	5,578
Individually evaluated for impairment			2,658	3,125
Collectively evaluated for impairment			513,538	493,617
Total gross loans			516,196	496,742
Residential Portfolio Segment [Member]
Balance	1,716	1,577
Charge-offs	(169)	(73)
Recoveries	75	8
Provision	(132)	449
Balance	1,490	1,961
Individually evaluated for impairment			628	721
Collectively evaluated for impairment			862	995
Total	1,716	1,577	1,490	1,716
Individually evaluated for impairment			10,785	11,894
Collectively evaluated for impairment			86,155	90,050
Total gross loans			96,940	101,944
Consumer Portfolio Segment [Member]
Balance	955	770
Charge-offs	(227)	(143)
Recoveries	43	54
Provision	303	133
Balance	1,074	814
Individually evaluated for impairment			13	14
Collectively evaluated for impairment			1,061	941
Total	955	770	1,074	955
Individually evaluated for impairment			39	250
Collectively evaluated for impairment			51,384	51,431
Total gross loans			51,423	51,681
Unallocated Financing Receivables [Member]
Balance	446	556
Charge-offs
Recoveries
Provision	19	(194)
Balance	465	362
Individually evaluated for impairment
Collectively evaluated for impairment			465	446
Total	$ 446	$ 556	465	446
Individually evaluated for impairment
Collectively evaluated for impairment
Total gross loans

Financing receivable allowance for credit losses, provision.

No definition available.

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

- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

+ Details

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

- Definition

The valuation allowance for financing receivables that are expected to be uncollectible that were collectively evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

+ Details

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

- Definition

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-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

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of recovery of financing receivables doubtful of collection that were previously charged off.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(4)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

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

- Definition

Amount of direct write-downs of financing receivables charged against the allowance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesWriteOffs
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The balance of financing receivables that were collectively evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

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

- Definition

The balance of financing receivables that were individually evaluated for impairment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

+ Details

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

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522

+ Details

Name:	us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
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_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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