Represent additional loan.

No definition available.

Name:	kffb_AdditionalLoan
Namespace Prefix:	kffb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of Financial instruments for TDRs

+ References

No definition available.

+ Details

Name:	kffb_FinancingReceivableModificationsPostModificationRecordedInvestment
Namespace Prefix:	kffb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Loans receivable, description.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

Represents the percentage of bankruptcy proceedings to borrower.

+ References

No definition available.

+ Details

Name:	kffb_PercentageOfBankruptcyProceedingsToBorrower
Namespace Prefix:	kffb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represent secondary mortgage loan.

+ References

No definition available.

+ Details

Name:	kffb_SecondaryMortgageLoan
Namespace Prefix:	kffb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

For loans and debt securities, 1) for which at acquisition it was probable that the investor would be unable to collect all contractually required payments receivable, and 2) for which it is further probable that the investor will not be able to collect all cash flows expected at acquisition (plus any additional cash flows expected due to changes in estimate after acquisition), the allowance for credit losses recorded to reflect the impairment since acquisition.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5275-111524

+ Details

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

- Definition

Amount, after troubled debt restructuring, of modified financing receivable.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953676-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsPostModificationRecordedInvestment2
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	kffb_TroubledDebtRestructuringAxis=kffb_TroubledDebtRestructuringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans Receivable (Details Textual) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
Loans Receivable (Details Textual) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Jun. 30, 2019
Loans Receivable (Textual)
Net of a purchase credit discount	$ 351		$ 351
Loans receivable, description	One- to four-family loans in process of foreclosure totaled $860,000 and $1.2 million at December 31, and June 30, 2019, respectively.
Troubled Debt Restructuring [Member]
Loans Receivable (Textual)
Loans classified as TDRs	$ 1,900		$ 1,600
Bankruptcy proceedings, percentage	21.50%
Secondary mortgage loan		$ 219
Additional loan		30
TDRs