Amount of recovery of loans and lease receivables which had previously been fully or partially written-off as bad debts.

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

- Definition

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

+ References

+ Details

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

- Definition

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

+ References

+ 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

+ Details

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

- Definition

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

+ References

+ 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

+ Details

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

- Definition

Amount of financing receivable not past due.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953401-111524

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 55
-Paragraph 80
-URI http://asc.fasb.org/extlink&oid=121647567&loc=SL82922355-210448

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919253-210447

+ Details

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=121614798&loc=d3e15032-111544

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

+ Details

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

- Definition

Amount of expense related to estimated loss from loan and lease transactions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

+ Details

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

- Details

Name:	us-gaap_CreditLossStatusAxis=cbkm_FinancialAssetAcquiredMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditLossStatusAxis=us-gaap_FinancialAssetOriginatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- 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:

Note 4 - Loans - Allowance for Loan Losses by Portfolio Segment (Details) - USD ($) $ in Thousands	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Beginning balance	$ 3,788	$ 3,422
Provision for loan losses	1,980	(440)
Loans charged-off	(146)	(116)
Recoveries	56	922
Total ending allowance balance	5,678	3,788
Individually evaluated for impairment			$ 34	$ 9
Collectively evaluated for impairment				3,779
Total ending allowance balance	3,788	3,422	5,678	3,788
Loans individually evaluated for impairment			1,923	1,189
Loans collectively evaluated for impairment				368,877
Total ending loans balance			544,797	370,066
Financial Asset Acquired [Member]
Collectively evaluated for impairment			197
Loans collectively evaluated for impairment			48,969
Financial Asset Originated [Member]
Collectively evaluated for impairment			5,447
Loans collectively evaluated for impairment			493,905
Commercial Portfolio Segment [Member]
Beginning balance	660	586
Provision for loan losses	287	74
Loans charged-off
Recoveries
Total ending allowance balance	947	660
Individually evaluated for impairment			28	2
Collectively evaluated for impairment				658
Total ending allowance balance	947	586	947	660
Loans individually evaluated for impairment			179	174
Loans collectively evaluated for impairment				80,413
Total ending loans balance			157,328	80,587
Commercial Portfolio Segment [Member] \| Financial Asset Acquired [Member]
Collectively evaluated for impairment
Loans collectively evaluated for impairment			1,095
Commercial Portfolio Segment [Member] \| Financial Asset Originated [Member]
Collectively evaluated for impairment			919
Loans collectively evaluated for impairment			156,054
Commercial Real Estate Portfolio Segment [Member]
Beginning balance	2,575	2,277
Provision for loan losses	1,044	(498)
Loans charged-off		(80)
Recoveries	4	876
Total ending allowance balance	3,623	2,575
Individually evaluated for impairment			6	7
Collectively evaluated for impairment				2,568
Total ending allowance balance	3,623	2,277	3,623	2,575
Loans individually evaluated for impairment			1,045	658
Loans collectively evaluated for impairment				210,709
Total ending loans balance			245,957	211,367
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset Acquired [Member]
Collectively evaluated for impairment			103
Loans collectively evaluated for impairment			8,072
Commercial Real Estate Portfolio Segment [Member] \| Financial Asset Originated [Member]
Collectively evaluated for impairment			3,514
Loans collectively evaluated for impairment			236,840
Residential Portfolio Segment [Member]
Beginning balance	494	499
Provision for loan losses	497	(28)
Loans charged-off	(6)
Recoveries	4	23
Total ending allowance balance	989	494
Individually evaluated for impairment
Collectively evaluated for impairment				494
Total ending allowance balance	989	499	989	494
Loans individually evaluated for impairment			699	357
Loans collectively evaluated for impairment				72,591
Total ending loans balance			120,119	72,948
Residential Portfolio Segment [Member] \| Financial Asset Acquired [Member]
Collectively evaluated for impairment			94
Loans collectively evaluated for impairment			27,252
Residential Portfolio Segment [Member] \| Financial Asset Originated [Member]
Collectively evaluated for impairment			895
Loans collectively evaluated for impairment			92,168
Consumer Portfolio Segment [Member]
Beginning balance	59	60
Provision for loan losses	152	12
Loans charged-off	(140)	(36)
Recoveries	48	23
Total ending allowance balance	119	59
Individually evaluated for impairment
Collectively evaluated for impairment				59
Total ending allowance balance	$ 119	$ 60	119	59
Loans individually evaluated for impairment
Loans collectively evaluated for impairment				5,164
Total ending loans balance			21,393	$ 5,164
Consumer Portfolio Segment [Member] \| Financial Asset Acquired [Member]
Collectively evaluated for impairment
Loans collectively evaluated for impairment			12,550
Consumer Portfolio Segment [Member] \| Financial Asset Originated [Member]
Collectively evaluated for impairment			119
Loans collectively evaluated for impairment			$ 8,843