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ALLOWANCE FOR CREDIT LOSSES - Allowance for Credit Losses and Balance of Loans Receivable (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	$ 44,867	$ 46,872	$ 48,734	$ 48,877	$ 47,613	$ 47,058
Loans individually analyzed	28,100
Financing receivable, before allowance for credit loss, fee and loan in process	5,756,938		5,850,476
Unaccreted yield adjustments	(11,309)		(21,055)
Loans receivable	5,745,629		5,829,421
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, before allowance for credit loss, fee and loan in process	3,964,628		4,103,819
Commercial \| Multi-family mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	24,462	25,590	26,362	27,498	26,246	25,321
Financing receivable, before allowance for credit loss, fee and loan in process	2,651,274		2,761,775
Commercial \| Nonresidential mortgage
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	5,888	7,437	8,953	8,593	9,152	10,590
Financing receivable, before allowance for credit loss, fee and loan in process	947,287		968,574
Commercial \| Commercial business
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	1,293	1,413	1,440	1,819	1,972	1,792
Financing receivable, before allowance for credit loss, fee and loan in process	144,134		146,861
Commercial \| Construction
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	1,171	1,317	1,336	1,201	1,120	1,486
Financing receivable, before allowance for credit loss, fee and loan in process	221,933		226,609
Residential
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	11,653	10,703	10,237	9,355	8,801	7,540
Financing receivable, before allowance for credit loss, fee and loan in process	1,746,065		1,700,559
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, before allowance for credit loss, fee and loan in process	46,245		46,098
Consumer \| Home equity loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	330	342	338	339	244	245
Financing receivable, before allowance for credit loss, fee and loan in process	43,517		43,549
Consumer \| Other consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Financing receivable, allowance for credit loss, excluding accrued interest	70	$ 70	68	$ 72	$ 78	$ 84
Financing receivable, before allowance for credit loss, fee and loan in process	2,728		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	165		211
Loans individually analyzed	1,790		928
Loans collectively evaluated	16,210		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	38		70
Loans individually analyzed	313		333
Loans collectively evaluated	2,269		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	42		9
Loans individually analyzed	0		0
Loans collectively evaluated	4,774		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	85		132
Loans individually analyzed	1,452		570
Loans collectively evaluated	3,432		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	154		3,417
Loans acquired with deteriorated credit quality collectively evaluated	44,548		45,103
Loans individually analyzed	26,299		41,699
Loans collectively evaluated	5,712,639		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	35		326
Loans acquired with deteriorated credit quality collectively evaluated	24,427		26,036
Loans individually analyzed	15,988		19,114
Loans collectively evaluated	2,635,286		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	0		3,001
Loans acquired with deteriorated credit quality collectively evaluated	5,850		5,882
Loans individually analyzed	4,022		16,207
Loans collectively evaluated	940,683		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	106		20
Loans acquired with deteriorated credit quality collectively evaluated	1,145		1,411
Loans individually analyzed	815		252
Loans collectively evaluated	138,545		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	1,171		1,336
Loans individually analyzed	0		0
Loans collectively evaluated	216,198		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	13		70
Loans acquired with deteriorated credit quality collectively evaluated	11,555		10,032
Loans individually analyzed	5,452		6,101
Loans collectively evaluated	1,735,729		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	330		338
Loans individually analyzed	22		25
Loans collectively evaluated	43,470		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	$ 2,728		$ 2,549