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Earnings Per Share (Details Textual) - shares | 9 Months Ended
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Mar. 31, 2020 | Mar. 31, 2019
Earnings Per Share (Textual) |  |
Stock option shares outstanding |  |

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- Definition Earnings Per Share (Textual). + References No definition available. + Details
Name: | kffb_EarningsPerShareTextualAbstract
Namespace Prefix: | kffb_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Stock option shares outstanding. + References No definition available. + Details
Name: | kffb_StockOptionSharesOutstanding
Namespace Prefix: | kffb_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration