Financing receivable number of non TDR deferred loans contracts.

No definition available.

Name:	krny_FinancingReceivableNumberOfNonTDRDeferredLoansContracts
Namespace Prefix:	krny_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Financing receivable TDR modified principal balance.

+ References

No definition available.

+ Details

Name:	krny_FinancingReceivableTDRModifiedPrincipalBalance
Namespace Prefix:	krny_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Financing receivables individually analyzed loans carrying value .

+ References

No definition available.

+ Details

Name:	krny_FinancingReceivablesIndividuallyAnalyzedLoansCarryingValue
Namespace Prefix:	krny_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing receivables individually analyzed loans collateral dependent.

+ References

No definition available.

+ Details

Name:	krny_FinancingReceivablesIndividuallyAnalyzedLoansCollateralDependent
Namespace Prefix:	krny_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Mortgage loans in process of foreclosure, number of loans.

+ References

No definition available.

+ Details

Name:	krny_MortgageLoansInProcessOfForeclosureNumberOfLoans
Namespace Prefix:	krny_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of new loans to related parties.

+ References

No definition available.

+ Details

Name:	krny_NumberOfNewLoansToRelatedParties
Namespace Prefix:	krny_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Provisions for uncertainty.

+ References

No definition available.

+ Details

Name:	krny_ProvisionsForUncertainty
Namespace Prefix:	krny_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Provisions for uncertainty expiration date.

+ References

No definition available.

+ Details

Name:	krny_ProvisionsForUncertaintyExpirationDate
Namespace Prefix:	krny_
Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of allowance for credit loss on financing receivable. Excludes allowance for financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7)(2))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=124255206&loc=SL82895884-210446

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=124255953&loc=SL82919249-210447

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (3)

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (c)

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph (a)
-Subparagraph (1)

+ Details

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

- Definition

Amount of financing receivable modified as troubled debt restructuring within previous 12 months, with subsequent payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL6953682-111524

+ Details

Name:	us-gaap_FinancingReceivableModificationsSubsequentDefaultRecordedInvestment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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=121585226&loc=d3e18845-111554

+ Details

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

- Definition

For an unclassified balance sheet, reflects the carrying amount of unpaid loan amounts due from related parties at the balance sheet date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(e))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

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

- Definition

Reflects the amount of new advances made to related parties in the form of loan and lease receivables.

+ References

+ Details

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

- Definition

Recorded investment of consumer mortgage loan receivables secured by residential real estate properties for which formal foreclosure proceedings are in process.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=123577603&loc=SL49126937-111524

+ Details

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

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfRealEstateProperties
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of land and buildings obtained through foreclosure proceedings or defeasance in full or partial satisfaction of a debt arrangement.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=123577603&loc=d3e5162-111524

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=124259787&loc=d3e4437-111522

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_SingleFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_RealEstateAcquiredInSatisfactionOfDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_UnusualRiskOrUncertaintyByNatureAxis=krny_CARESMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoanRestructuringModificationAxis=krny_TroubledDebtRestructuringsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans Receivable - Additional Information (Detail)		12 Months Ended
Loans Receivable - Additional Information (Detail)	Dec. 27, 2020 USD ($)	Jun. 30, 2022 USD ($) Loan Property	Jun. 30, 2021 USD ($) Loan Property
Financing Receivable Recorded Investment [Line Items]
Loans and leases receivable, related parties		$ 2,600,000	$ 1,400,000
Number of new loans to related parties \| Loan		2,000,000	1,000,000
Loans and leases receivable, related parties, additions		$ 1,800,000	$ 478,000
Financing receivable TDR modified principal balance		22,200,000	17,800,000
Loans acquired with deteriorated credit quality		47,058,000	58,165,000
TDR charge-offs		0	0
TDR defaults		305,000	$ 0
Relief provisions		$ 900,000,000,000
Relief provision expiration date		Dec. 31, 2020
Number of deferred non-TDR loans \| Loan		0
Financing receivables individually analyzed loans carrying value		$ 70,300,000
Financing receivables individually analyzed loans collateral dependent		63,300,000
Residential Mortgage [Member]
Financing Receivable Recorded Investment [Line Items]
Number of loans in process of foreclosure \| Loan			11
Mortgage loans in process of foreclosure, carrying value		1,500,000	$ 2,100,000
Residential Mortgage [Member] \| Single-family Property [Member]
Financing Receivable Recorded Investment [Line Items]
Aggregate carrying value of real estate owned		$ 178,000,000	$ 178,000,000
Real Estate Acquired in Satisfaction of Debt [Member] \| Residential Mortgage [Member] \| Single-family Property [Member]
Financing Receivable Recorded Investment [Line Items]
Number of properties held \| Property		1	1
CARES Act [Member]
Financing Receivable Recorded Investment [Line Items]
Relief provisions	$ 900,000,000,000
CARES Act [Member] \| Maximum [Member]
Financing Receivable Recorded Investment [Line Items]
Relief provision expiration date	Jan. 01, 2022
CARES Act [Member] \| Minimum [Member]
Financing Receivable Recorded Investment [Line Items]
Relief provision expiration date	Dec. 31, 2020
Troubled Debt Restructurings [Member]
Financing Receivable Recorded Investment [Line Items]
Loans acquired with deteriorated credit quality		$ 365,000	$ 256,000