Note 3 - Securities (Details Textual) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Available-for-sale Securities Income Tax Provision on Gross Realized Gains	$ 2	$ 1	$ 2	$ 22

This item represents the tax provision (benefit) applicable to gross profit (loss) realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

No definition available.

Name:	cbkm_AvailableForSaleSecuritiesIncomeTaxProvisionOnGrossRealizedGains
Namespace Prefix:	cbkm_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration