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Deposits (Details) - USD ($) | Jun. 30, 2020 | Jun. 30, 2019
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Disclosure Text Block [Abstract] |  |
Deposits | $ 250,000 |
Certificate of deposit accounts with balances equal to or in exceeding of $250,000 totaling | $ 13,000,000 | $ 9,800,000

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- Definition BankDeposits + References No definition available. + Details
Name: | kffb_BankDeposits
Namespace Prefix: | kffb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition TimeDeposits250000OrMore + References No definition available. + Details
Name: | kffb_TimeDeposits250000OrMore
Namespace Prefix: | kffb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_DisclosureTextBlockAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration