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LOANS AND ALLOWANCE FOR CREDIT LOSSES - Loan Summary (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Loans receivable, net
Loans	$ 10,432,365	$ 9,704,598
Allowance for credit losses	(79,114)	(66,669)
Loans, net of allowance for credit losses	10,353,251	9,637,929
Net deferred loan origination costs	84,100	81,600
Loans receivable, related parties
Balance at beginning of year	11,692	12,373
New loans	0	1,372
Payments	(1,157)	(2,053)
Balance at end of year	10,535	11,692
CRE - multifamily
Loans receivable, net
Loans	724,114	619,794
CRE - owner occupied
Loans receivable, net
Loans	864,783	752,774
CRE - non-owner occupied
Loans receivable, net
Loans	1,775,099	1,711,198
Commercial & industrial and other business loans
Loans receivable, net
Loans	1,141,182	1,000,630
Consumer mortgage
Loans receivable, net
Loans	3,489,780	3,285,018
Consumer indirect
Loans receivable, net
Loans	1,767,655	1,703,440
Consumer direct
Loans receivable, net
Loans	192,327	185,229
Home equity
Loans receivable, net
Loans	477,425	446,515
Commercial Portfolio Segment \| CRE - multifamily
Loans receivable, net
Loans	724,114	619,794
Commercial Portfolio Segment \| CRE - owner occupied
Loans receivable, net
Loans	864,783	752,774
Commercial Portfolio Segment \| CRE - non-owner occupied
Loans receivable, net
Loans	1,775,099	1,711,198
Commercial Portfolio Segment \| Commercial & industrial and other business loans
Loans receivable, net
Loans	1,141,182	1,000,630
Residential Portfolio Segment \| Consumer mortgage
Loans receivable, net
Loans	3,489,780	3,285,018
Allowance for credit losses	(15,017)	(15,333)	$ (14,343)	$ (10,017)
Residential Portfolio Segment \| Home equity
Loans receivable, net
Allowance for credit losses	(1,548)	(1,628)	(1,594)	(1,814)
Consumer Portfolio Segment \| Consumer indirect
Loans receivable, net
Loans	1,767,655	1,703,440
Allowance for credit losses	(20,895)	(18,585)	(17,852)	(11,737)
Consumer Portfolio Segment \| Consumer direct
Loans receivable, net
Loans	192,327	185,229
Allowance for credit losses	(3,453)	(3,269)	$ (2,973)	$ (2,306)
Consumer Portfolio Segment \| Home equity
Loans receivable, net
Loans	$ 477,425	$ 446,515