Amount excluding accrued interest, of allowance for credit loss on financing receivable. Excludes net investment in lease.

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

- Definition

Amount of allowance for credit loss on financing receivable evaluated on collective basis. Excludes financing receivable evaluated on individual basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.5.a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480418/310-10-S99-4

Reference 2: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 11B
-Subparagraph (g)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-11B

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 30
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479391/326-20-30-2

+ Details

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

- Definition

Amount of allowance for credit loss on financing receivable evaluated on individual basis. Excludes financing receivable evaluated on collective basis.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (e)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 13
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-13

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

+ Details

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

- Definition

Amortized cost, before allowance for credit loss, fee, and loan in process, of financing receivable. Excludes financing receivable covered under loss sharing agreement and net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-2

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

+ Details

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

- Definition

Amount of financing receivable collectively evaluated for credit loss. Excludes financing receivable individually evaluated for credit loss.

+ References

+ Details

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

- Definition

Amortized cost excluding accrued interest, before allowance for credit loss, of financing receivable. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479344/326-20-45-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-5

+ Details

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

- Definition

Amount of financing receivable individually evaluated for credit loss. Excludes financing receivable collectively evaluated for credit loss.

+ References

+ Details

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

- Definition

Amount of unamortized loan commitment, origination, and other costs (fees) and purchase premium (discount) on financing receivable recognized as adjustment to yield. Excludes financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481598/310-20-45-1

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 4
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-4

Reference 3: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-SubTopic 20
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481569/310-20-50-3

+ Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=krny_MultiFamilyMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=krny_NonresidentialMortgageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_ConstructionLoansMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_HomeEquityLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=krny_OtherConsumerLoansMember
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:	us-gaap_CreditLossStatusAxis=us-gaap_FinancialAssetOtherThanFinancialAssetAcquiredWithCreditDeteriorationMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

ALLOWANCE FOR CREDIT LOSSES - Allowance for Credit Losses and Balance of Loans Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	$ 44,723	$ 44,958	$ 46,191	$ 44,455	$ 44,457	$ 44,939
Loans individually analyzed	52,400
Financing receivable, before allowance for credit loss, fee and loan in process	5,781,244		5,814,539
Unaccreted yield adjustments	(2,063)		(1,602)
Loans receivable	5,779,181		5,812,937
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, before allowance for credit loss, fee and loan in process	3,976,465		4,012,678
Commercial \| Multi-family mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	23,050	24,171	24,906	24,660	24,880	24,125
Financing receivable, before allowance for credit loss, fee and loan in process	2,555,001		2,709,654
Commercial \| Nonresidential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	7,802	7,871	6,938	6,676	6,479	6,125
Financing receivable, before allowance for credit loss, fee and loan in process	1,012,422		986,556
Commercial \| Commercial business
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	2,618	1,984	2,428	1,517	1,563	1,573
Financing receivable, before allowance for credit loss, fee and loan in process	201,277		138,755
Commercial \| Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	1,437	1,284	1,155	1,123	1,157	1,230
Financing receivable, before allowance for credit loss, fee and loan in process	207,765		177,713
Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	9,217	9,075	10,180	9,958	9,855	11,461
Financing receivable, before allowance for credit loss, fee and loan in process	1,741,023		1,748,591
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, before allowance for credit loss, fee and loan in process	63,756		53,270
Consumer \| Home equity loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	499	466	490	417	421	349
Financing receivable, before allowance for credit loss, fee and loan in process	61,379		50,737
Consumer \| Other consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	100	$ 107	94	$ 104	$ 102	$ 76
Financing receivable, before allowance for credit loss, fee and loan in process	2,377		2,533
Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		45
Loans acquired with deteriorated credit quality collectively evaluated	104		130
Loans individually analyzed	782		875
Loans collectively evaluated	10,876		11,784
Receivables Acquired with Deteriorated Credit Quality \| Commercial \| Multi-family mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		0
Loans acquired with deteriorated credit quality collectively evaluated	0		0
Loans individually analyzed	0		0
Loans collectively evaluated	0		0
Receivables Acquired with Deteriorated Credit Quality \| Commercial \| Nonresidential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		0
Loans acquired with deteriorated credit quality collectively evaluated	15		20
Loans individually analyzed	219		240
Loans collectively evaluated	1,012		1,405
Receivables Acquired with Deteriorated Credit Quality \| Commercial \| Commercial business
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		0
Loans acquired with deteriorated credit quality collectively evaluated	6		23
Loans individually analyzed	0		0
Loans collectively evaluated	711		1,093
Receivables Acquired with Deteriorated Credit Quality \| Commercial \| Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		0
Loans acquired with deteriorated credit quality collectively evaluated	0		0
Loans individually analyzed	0		0
Loans collectively evaluated	5,735		5,735
Receivables Acquired with Deteriorated Credit Quality \| Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		34
Loans acquired with deteriorated credit quality collectively evaluated	83		87
Loans individually analyzed	554		614
Loans collectively evaluated	3,418		3,551
Receivables Acquired with Deteriorated Credit Quality \| Consumer \| Home equity loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		11
Loans acquired with deteriorated credit quality collectively evaluated	0		0
Loans individually analyzed	9		21
Loans collectively evaluated	0		0
Receivables Acquired with Deteriorated Credit Quality \| Consumer \| Other consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		0
Loans acquired with deteriorated credit quality collectively evaluated	0		0
Loans individually analyzed	0		0
Loans collectively evaluated	0		0
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	956		2,440
Loans acquired with deteriorated credit quality collectively evaluated	43,663		43,576
Loans individually analyzed	51,597		44,722
Loans collectively evaluated	5,717,989		5,757,158
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Commercial \| Multi-family mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	886		1,377
Loans acquired with deteriorated credit quality collectively evaluated	22,164		23,529
Loans individually analyzed	38,116		30,857
Loans collectively evaluated	2,516,885		2,678,797
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Commercial \| Nonresidential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		0
Loans acquired with deteriorated credit quality collectively evaluated	7,787		6,918
Loans individually analyzed	5,460		5,523
Loans collectively evaluated	1,005,731		979,388
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Commercial \| Commercial business
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	45		971
Loans acquired with deteriorated credit quality collectively evaluated	2,567		1,434
Loans individually analyzed	536		2,223
Loans collectively evaluated	200,030		135,439
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Commercial \| Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		0
Loans acquired with deteriorated credit quality collectively evaluated	1,437		1,155
Loans individually analyzed	2,755		0
Loans collectively evaluated	199,275		171,978
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	25		60
Loans acquired with deteriorated credit quality collectively evaluated	9,109		9,999
Loans individually analyzed	4,542		5,936
Loans collectively evaluated	1,732,509		1,738,490
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Consumer \| Home equity loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		32
Loans acquired with deteriorated credit quality collectively evaluated	499		447
Loans individually analyzed	188		183
Loans collectively evaluated	61,182		50,533
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Consumer \| Other consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Related Allowance	0		0
Loans acquired with deteriorated credit quality collectively evaluated	100		94
Loans individually analyzed	0		0
Loans collectively evaluated	$ 2,377		$ 2,533