Disclosures About Fair Value of Assets and Liabilities (Details) - Schedule of foregoing methods and assumptions, the carrying value and fair value - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020
Financial assets
Federal Home Loan Bank stock	$ 6,498	$ 6,498
Financial liabilities
Advances by borrowers for taxes and insurance	1,084	800
Total [Member]
Financial assets
Cash and cash equivalents	17,116	13,702
Time deposits in other financial institutions	1,254	2,252
Available-for-sale securities	36	541
Held-to-maturity securities	582	611
Loans held for sale	1,064	685
Loans receivable - net	300,232	295,431
Federal Home Loan Bank stock
Accrued interest receivable	700	830
Financial liabilities
Deposits	215,928	213,118
Federal Home Loan Bank advances	59,140	55,416
Advances by borrowers for taxes and insurance	1,084	800
Accrued interest payable	24	27
Carrying Value [Member]
Financial assets
Cash and cash equivalents	17,116	13,702
Time deposits in other financial institutions	1,241	2,229
Available-for-sale securities	36	541
Held-to-maturity securities	564	598
Loans held for sale	1,035	667
Loans receivable - net	290,509	285,887
Federal Home Loan Bank stock	6,498	6,498
Accrued interest receivable	700	830
Financial liabilities
Deposits	215,102	212,273
Federal Home Loan Bank advances	58,392	54,715
Advances by borrowers for taxes and insurance	1,084	800
Accrued interest payable	24	27
Level 1 [Member]
Financial assets
Cash and cash equivalents	17,116	13,702
Time deposits in other financial institutions	1,254	2,252
Available-for-sale securities
Held-to-maturity securities
Loans held for sale
Loans receivable - net
Federal Home Loan Bank stock
Accrued interest receivable
Financial liabilities
Deposits	84,030	78,118
Federal Home Loan Bank advances
Advances by borrowers for taxes and insurance
Accrued interest payable
Level 2 [Member]
Financial assets
Cash and cash equivalents
Time deposits in other financial institutions
Available-for-sale securities	36	541
Held-to-maturity securities	582	611
Loans held for sale		685
Loans receivable - net
Federal Home Loan Bank stock
Accrued interest receivable	700	830
Financial liabilities
Deposits	131,898	135,000
Federal Home Loan Bank advances	59,140	55,416
Advances by borrowers for taxes and insurance	1,084	800
Accrued interest payable	24	27
Level 3 [Member]
Financial assets
Cash and cash equivalents
Time deposits in other financial institutions
Available-for-sale securities
Held-to-maturity securities
Loans held for sale	1,064
Loans receivable - net	300,232	295,431
Federal Home Loan Bank stock
Accrued interest receivable
Financial liabilities
Federal Home Loan Bank advances
Advances by borrowers for taxes and insurance
Accrued interest payable

No definition available.

Name:	kffb_AccruedInterestReceivable
Namespace Prefix:	kffb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Name:	kffb_DepositFairValueDisclosure
Namespace Prefix:	kffb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

Name:	kffb_FinancialAssetsAbstract
Namespace Prefix:	kffb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	kffb_FinancialLiabilitiesAbstract
Namespace Prefix:	kffb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	kffb_TimeDepositsInOtherFinancialInstitutions
Namespace Prefix:	kffb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value portion of trade and related party payables and accrued expenses.

+ References

No definition available.

+ Details

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

- Definition

Carrying amount of accumulated prepayments received by financial institutions from borrowers for taxes (for example, property taxes) and insurance (for example, property and catastrophe) which will periodically be remitted to the appropriate governmental agency or vendor on behalf of the borrower.

+ 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 210.9-03.15(5))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

Name:	us-gaap_AdvancePaymentsByBorrowersForTaxesAndInsurance
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

Name:	us-gaap_CashAndCashEquivalentsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

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

- Definition

Federal Home Loan Bank (FHLB) stock represents an equity interest in a FHLB. It does not have a readily determinable fair value because its ownership is restricted and it lacks a market (liquidity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 325
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=75031641&loc=d3e63345-112809

+ Details

Name:	us-gaap_FederalHomeLoanBankStock
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

Name:	us-gaap_LoansHeldForSaleFairValueDisclosure
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

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

- Definition

Fair value of securitized, pay-through debt securities collateralized by real estate mortgage loans classified as available-for-sale.

+ References

No definition available.

+ Details

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

- Definition

Fair value of securitized, pay-through debt securities collateralized by real estate mortgage loans classified as held-to-maturity.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_AssetsTotalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByMeasurementBasisAxis=us-gaap_CarryingReportedAmountFairValueDisclosureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: