Note 5 - Fair Value - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jun. 30, 2020
Held-to-maturity, fair value	$ 3,605	$ 3,868
Fair Value, Inputs, Level 1 [Member] \| Reported Value Measurement [Member]
Cash and cash equivalents	9,045	9,659
Fair Value, Inputs, Level 1 [Member] \| Estimate of Fair Value Measurement [Member]
Cash and cash equivalents	9,045	9,659
Fair Value, Inputs, Level 2 [Member] \| Reported Value Measurement [Member]
Certificates of deposit in other financial institutions	8,599	11,635
Loans held for sale	4,770	3,507
Accrued interest receivable	2,327	2,646
Short-term borrowings	13,275	6,943
Federal Home Loan Bank advances	18,083	31,161
Accrued interest payable	88	107
Fair Value, Inputs, Level 2 [Member] \| Reported Value Measurement [Member] \| Demand and Savings Deposits [Member]
Demand and savings deposits	540,811	517,973
Fair Value, Inputs, Level 2 [Member] \| Reported Value Measurement [Member] \| Time Deposits [Member]
Demand and savings deposits	107,551	115,382
Fair Value, Inputs, Level 2 [Member] \| Estimate of Fair Value Measurement [Member]
Certificates of deposit in other financial institutions	8,819	11,889
Loans held for sale	4,907	3,566
Accrued interest receivable	2,327	2,646
Short-term borrowings	13,275	6,943
Federal Home Loan Bank advances	18,423	31,571
Accrued interest payable	88	107
Fair Value, Inputs, Level 2 [Member] \| Estimate of Fair Value Measurement [Member] \| Demand and Savings Deposits [Member]
Demand and savings deposits	540,811	517,973
Fair Value, Inputs, Level 2 [Member] \| Estimate of Fair Value Measurement [Member] \| Time Deposits [Member]
Demand and savings deposits	108,158	116,238
Fair Value, Inputs, Level 3 [Member] \| Reported Value Measurement [Member]
Held-to-maturity, fair value	3,336	3,541
Loans, net	551,345	537,183
Fair Value, Inputs, Level 3 [Member] \| Estimate of Fair Value Measurement [Member]
Held-to-maturity, fair value	3,605	3,868
Loans, net	$ 565,397	$ 548,247

Fair value portion of accrued interest receivable.

No definition available.

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

- Definition

Fair value portion of certificates of deposits in other financial institutions.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of accrued expenses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

+ Details

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

- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

+ 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=120398452&loc=d3e534808-122878

+ Details

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

- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121645371&loc=SL120269820-111563

+ Details

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

- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

+ Details

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

- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-URI http://asc.fasb.org/subtopic&trid=2196772

+ Details

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

- Definition

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents the amount of short-term debt existing as of the balance sheet date.

+ References

No definition available.

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