Note 3 - Loans and Allowance for Credit Losses - Impaired Loans (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Dec. 31, 2022	Dec. 31, 2022	Jun. 30, 2023
Impaired Financing Receivable, Interest Income, Cash Basis Method	$ 10	$ 10	$ 558
Impaired Financing Receivable, Recorded Investment			405
Impaired Financing Receivable, Related Allowance			0
Impaired Financing Receivable, Average Recorded Investment	395	410
Impaired Financing Receivable, Interest Income, Accrual Method	10	24
Impaired Financing Receivable, Interest Income, Cash Basis Method		24
Commercial Portfolio Segment [Member]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance			404
Impaired Financing Receivable, with No Related Allowance, Recorded Investment			314
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	308	297
Impaired Financing Receivable, with No Related Allowance, Interest Income, Accrual Method	8	18
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	8	18
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance			404
Impaired Financing Receivable, with No Related Allowance, Recorded Investment			314
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	308	297
Impaired Financing Receivable, with No Related Allowance, Interest Income, Accrual Method	8	18
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	8	18
Commercial Real Estate Portfolio Segment [Member] \| Other Commercial Real Estate Loans [Member]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance			127
Impaired Financing Receivable, with No Related Allowance, Recorded Investment			88
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	40	40
Impaired Financing Receivable, with No Related Allowance, Interest Income, Accrual Method	1	4
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	1	4
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance			127
Impaired Financing Receivable, with No Related Allowance, Recorded Investment			88
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	40	40
Impaired Financing Receivable, with No Related Allowance, Interest Income, Accrual Method	1	4
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	1	4
Residential Portfolio Segment [Member] \| Owner Occupied Loans [Member]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance			24
Impaired Financing Receivable, with No Related Allowance, Recorded Investment			0
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	20	20
Impaired Financing Receivable, with No Related Allowance, Interest Income, Accrual Method	1	2
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	1	2
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance			24
Impaired Financing Receivable, with No Related Allowance, Recorded Investment			0
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	20	20
Impaired Financing Receivable, with No Related Allowance, Interest Income, Accrual Method	1	2
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	1	2
Residential Portfolio Segment [Member] \| Non-owner Occupied Loans [Member]
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance			3
Impaired Financing Receivable, with No Related Allowance, Recorded Investment			3
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	27	53
Impaired Financing Receivable, with No Related Allowance, Interest Income, Accrual Method	0	0
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	0	0
Impaired Financing Receivable, with No Related Allowance, Unpaid Principal Balance			3
Impaired Financing Receivable, with No Related Allowance, Recorded Investment			$ 3
Impaired Financing Receivable, with No Related Allowance, Average Recorded Investment	27	53
Impaired Financing Receivable, with No Related Allowance, Interest Income, Accrual Method	0	0
Impaired Financing Receivable, with No Related Allowance, Interest Income, Cash Basis Method	$ 0	$ 0

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-15

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-17

+ Details

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

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(2)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-15

+ Details

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

- Definition

Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-15

+ Details

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

- 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
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-14A

+ Details

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

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-15

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(4)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-15

+ Details

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

- Definition

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables that are recognized as impaired, for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of interest income, recognized on cash basis, on financing receivables, for which there is no related allowance for credit losses and are recognized as impaired.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbkm_OtherCommercialRealEstateMember
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_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=cbkm_OwnerOccupiedLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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