Note 8 - Federal Home Loan Bank Advances - Summary of Federal Home Loan Bank (FHLB) Advances (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Jun. 30, 2018
FHLB advance amount	$ 22,700
Fixed Rate Amortizing FHLB Advances [Member]
FHLB advance amount		$ 56
Weighted average rate		4.30%
Fixed Rate Amortizing FHLB Advances [Member] \| Minimum [Member]
Stated Interest rate range
Fixed Rate Amortizing FHLB Advances [Member] \| Maximum [Member]
Stated Interest rate range
Fixed Rate FHLB Advances [Member]
FHLB advance amount	$ 11,200	$ 11,700
Weighted average rate	1.59%	1.46%
Fixed Rate FHLB Advances [Member] \| Minimum [Member]
Stated Interest rate range	1.18%
Fixed Rate FHLB Advances [Member] \| Maximum [Member]
Stated Interest rate range	1.97%
Variable Rate FHLB Advances [Member]
Stated Interest rate range	2.56%
FHLB advance amount	$ 11,500
Weighted average rate	2.56%

Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.

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

- Definition

The calculated weighted average interest rate for Federal Home Loan Bank advances outstanding as of the Balance Sheet date.

+ 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 210.9-03.13(3)(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

Name:	us-gaap_FederalHomeLoanBankAdvancesActivityForYearAverageInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

States the interest rate applicable to Federal Home Loan Bank advances outstanding as of the Balance Sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

+ Details

Name:	us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresInterestRateAtPeriodEnd
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=cbkm_FixedRateAmortizingFHLBAdvancesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=cbkm_FixedRateFHLBAdvancesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=cbkm_VariableRateFHLBAdvancesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: