Note 15 - Fair Value (Details Textual) - USD ($) $ in Thousands	12 Months Ended
Jun. 30, 2019	Jun. 30, 2020
Other Real Estate Owned, Fair Value Disclosure	$ 0	$ 0
Impaired Financing Receivable, Related Allowance	9	34
Impaired Financing Receivable, Recorded Investment, Total	1,189	1,923
Fair Value, Nonrecurring [Member] \| Impaired Loans [Member]
Impaired Financing Receivable, Related Allowance	0	$ 0
Impaired Financing Receivable, Recorded Investment, Total	59
Allowance for Loan and Lease Losses, Period Increase (Decrease), Total	$ 80

Fair value portion of other real estate owned.

No definition available.

Name:	cbkm_OtherRealEstateOwnedFairValueDisclosure
Namespace Prefix:	cbkm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of increase (decrease) of allowance reserve for credit loss.

+ References

No definition available.

+ Details

Name:	us-gaap_AllowanceForLoanAndLeaseLossesPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953550-111524

+ Details

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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5212-111524

+ Details

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

- Details

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

- Details

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