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ALLOWANCE FOR CREDIT LOSSES - Allowance for Credit Losses and Balance of Loans Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Jun. 30, 2023	Sep. 30, 2022	Jun. 30, 2022
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	$ 46,872	$ 48,734	$ 47,613	$ 47,058
Loans individually analyzed	37,900
Financing receivable, before allowance for credit loss, fee and loan in process	5,760,475	5,850,476
Unaccreted yield adjustments	(24,426)	(21,055)
Loans receivable	5,736,049	5,829,421
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, before allowance for credit loss, fee and loan in process	4,025,884	4,103,819
Commercial \| Multi-family mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	25,590	26,362	26,246	25,321
Financing receivable, before allowance for credit loss, fee and loan in process	2,699,151	2,761,775
Commercial \| Nonresidential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	7,437	8,953	9,152	10,590
Financing receivable, before allowance for credit loss, fee and loan in process	946,801	968,574
Commercial \| Commercial business
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	1,413	1,440	1,972	1,792
Financing receivable, before allowance for credit loss, fee and loan in process	149,229	146,861
Commercial \| Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	1,317	1,336	1,120	1,486
Financing receivable, before allowance for credit loss, fee and loan in process	230,703	226,609
Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	10,703	10,237	8,801	7,540
Financing receivable, before allowance for credit loss, fee and loan in process	1,689,051	1,700,559
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, before allowance for credit loss, fee and loan in process	45,540	46,098
Consumer \| Home equity loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	342	338	244	245
Financing receivable, before allowance for credit loss, fee and loan in process	42,896	43,549
Consumer \| Other consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	70	68	$ 78	$ 84
Financing receivable, before allowance for credit loss, fee and loan in process	2,644	2,549
Receivables Acquired with Deteriorated Credit Quality
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	0	3
Loans acquired with deteriorated credit quality collectively evaluated	225	211
Loans individually analyzed	1,504	928
Loans collectively evaluated	17,850	17,967
Receivables Acquired with Deteriorated Credit Quality \| Commercial \| Multi-family mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	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]
Financing receivable, allowance for credit losses, individually evaluated for impairment	0	0
Loans acquired with deteriorated credit quality collectively evaluated	64	70
Loans individually analyzed	323	333
Loans collectively evaluated	3,492	3,562
Receivables Acquired with Deteriorated Credit Quality \| Commercial \| Commercial business
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	0	0
Loans acquired with deteriorated credit quality collectively evaluated	62	9
Loans individually analyzed	0	0
Loans collectively evaluated	4,852	4,237
Receivables Acquired with Deteriorated Credit Quality \| Commercial \| Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	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]
Financing receivable, allowance for credit losses, individually evaluated for impairment	0	3
Loans acquired with deteriorated credit quality collectively evaluated	99	132
Loans individually analyzed	1,156	570
Loans collectively evaluated	3,771	4,433
Receivables Acquired with Deteriorated Credit Quality \| Consumer \| Home equity loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	0	0
Loans acquired with deteriorated credit quality collectively evaluated	0	0
Loans individually analyzed	25	25
Loans collectively evaluated	0	0
Receivables Acquired with Deteriorated Credit Quality \| Consumer \| Other consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	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]
Financing receivable, allowance for credit losses, individually evaluated for impairment	1,851	3,417
Loans acquired with deteriorated credit quality collectively evaluated	44,796	45,103
Loans individually analyzed	36,408	41,699
Loans collectively evaluated	5,704,713	5,789,882
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Commercial \| Multi-family mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	342	326
Loans acquired with deteriorated credit quality collectively evaluated	25,248	26,036
Loans individually analyzed	16,266	19,114
Loans collectively evaluated	2,682,885	2,742,661
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Commercial \| Nonresidential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	1,407	3,001
Loans acquired with deteriorated credit quality collectively evaluated	5,966	5,882
Loans individually analyzed	14,598	16,207
Loans collectively evaluated	928,388	948,472
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Commercial \| Commercial business
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	36	20
Loans acquired with deteriorated credit quality collectively evaluated	1,315	1,411
Loans individually analyzed	437	252
Loans collectively evaluated	143,940	142,372
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Commercial \| Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	0	0
Loans acquired with deteriorated credit quality collectively evaluated	1,317	1,336
Loans individually analyzed	0	0
Loans collectively evaluated	224,968	220,874
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	66	70
Loans acquired with deteriorated credit quality collectively evaluated	10,538	10,032
Loans individually analyzed	5,085	6,101
Loans collectively evaluated	1,679,039	1,689,455
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Consumer \| Home equity loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	0	0
Loans acquired with deteriorated credit quality collectively evaluated	342	338
Loans individually analyzed	22	25
Loans collectively evaluated	42,849	43,499
Financial Asset, Other than Financial Asset Acquired with Credit Deterioration \| Consumer \| Other consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit losses, individually evaluated for impairment	0	0
Loans acquired with deteriorated credit quality collectively evaluated	70	68
Loans individually analyzed	0	0
Loans collectively evaluated	$ 2,644	$ 2,549