Loans (Details Textual) - USD ($) $ in Thousands	12 Months Ended
Jun. 30, 2018	Jun. 30, 2017
Loans Receivable [Line Items]
Net of a credit quality component	$ 383	$ 388
Loans on nonaccrual, TDR	1,500	1,200
Troubled debt restructurings	93
Loans acquired credit quality	1,100	1,700
Nonaccrual loan	5,246	5,029
Loans past due over 90 days and still accruing of loans acquired	2,419	1,781
Total past due	8,311	11,037
30-89 Days Past Due [Member]
Loans Receivable [Line Items]
Total past due	3,986	6,397
Greater than 90 Days Past Due [Member]
Loans Receivable [Line Items]
Total past due	4,325	4,640
Financial Asset Acquired with Credit Deterioration [Member]
Loans Receivable [Line Items]
Nonaccrual loan	764	566
Loans past due over 90 days and still accruing of loans acquired	374	486
Residential Real Estate One to Four Family [Member]
Loans Receivable [Line Items]
Troubled debt restructurings	440	99
Nonaccrual loan	4,210	4,870
Loans past due over 90 days and still accruing of loans acquired	2,419	1,770
Total past due	7,233	9,689
Residential Real Estate One to Four Family [Member] \| 30-89 Days Past Due [Member]
Loans Receivable [Line Items]
Total past due	3,182	5,193
Residential Real Estate One to Four Family [Member] \| Greater than 90 Days Past Due [Member]
Loans Receivable [Line Items]
Total past due	4,051	4,496
Residential Real Estate Loan One [Member]
Loans Receivable [Line Items]
Troubled debt restructurings	23
Residential Real Estate Loan Two [Member]
Loans Receivable [Line Items]
Troubled debt restructurings	325
Residential Real Estate Loan Four [Member]
Loans Receivable [Line Items]
Troubled debt restructurings	136
Troubled Debt Restructuring [Member] \| 30-89 Days Past Due [Member]
Loans Receivable [Line Items]
Total past due	277	25
Troubled Debt Restructuring [Member] \| Greater than 90 Days Past Due [Member]
Loans Receivable [Line Items]
Total past due	$ 371	$ 1,000

No definition available.

Name:	kffb_LoansReceivableLineItems
Namespace Prefix:	kffb_
Data Type:	xbrli:stringItemType
Balance Type:	na
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=84173941&loc=d3e5275-111524

+ Details

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

- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestment90DaysPastDueAndStillAccruing
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5111-111524

+ Details

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

- Definition

Recorded Investment in financing receivables that are past due at the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 7A
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953401-111524

+ Details

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

- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=82895541&loc=d3e18845-111554

+ Details

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

- Definition

Amount of investment in mortgage loan on real estate by entity with substantial portion of business acquiring and holding investment real estate or interest in real estate.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 948
-SubTopic 310
-Section S99
-Paragraph 1
-Subparagraph (SX 210.12-29(Column G))
-URI http://asc.fasb.org/extlink&oid=6589523&loc=d3e617274-123014

+ Details

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

- Definition

Net amount of the investment in a contractual right to receive money on demand or on fixed or determinable dates that is recognized as an asset in the creditor's statement of financial position. Examples include, but are not limited to, credit card receivables, notes receivable and receivables relating to lessor's rights to payments from leases other than operating leases that have been recorded as assets. Excludes trade accounts receivable with contractual maturity of one year or less and arose from the sale of goods or services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.3)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=kffb_FinancingReceivables30To89DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancingReceivablesEqualToGreaterThan90DaysPastDueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditLossStatusAxis=us-gaap_FinancialAssetAcquiredWithCreditDeteriorationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	kffb_ResidentialRealEstateFamilyAxis=kffb_ResidentialRealEstateOneToFourFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	kffb_ResidentialRealEstateFamilyAxis=kffb_ResidentiaLrealEstateLoanOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	kffb_ResidentialRealEstateFamilyAxis=kffb_ResidentiaLrealEstateLoanTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	kffb_ResidentialRealEstateFamilyAxis=kffb_ResidentialRealEstateLoanFourMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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