LOANS AND ALLOWANCE FOR CREDIT LOSSES - Loan Summary (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Mar. 31, 2026	Dec. 31, 2025	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024
Loans receivable, net
Loans	$ 11,282,824		$ 10,949,757
Allowance for credit losses	(91,696)		(87,921)	$ (81,900)
Loans, net of allowance for credit losses	11,191,128		10,861,836
CRE - multifamily
Loans receivable, net
Loans	951,856		917,586
CRE - owner occupied
Loans receivable, net
Loans	892,342		871,801
CRE - non-owner occupied
Loans receivable, net
Loans	1,848,158		1,670,451
Commercial & industrial and other business loans
Loans receivable, net
Loans	1,348,263		1,274,029
Consumer mortgage
Loans receivable, net
Loans	3,629,301		3,617,186
Consumer indirect
Loans receivable, net
Loans	1,871,343		1,859,354
Consumer direct
Loans receivable, net
Loans	202,387		205,595
Home equity
Loans receivable, net
Loans	539,174		533,755
Commercial Portfolio Segment \| CRE - multifamily
Loans receivable, net
Loans	951,856		917,586
Commercial Portfolio Segment \| CRE - owner occupied
Loans receivable, net
Loans	892,342		871,801
Commercial Portfolio Segment \| CRE - non-owner occupied
Loans receivable, net
Loans	1,848,158		1,670,451
Commercial Portfolio Segment \| Commercial & industrial and other business loans
Loans receivable, net
Loans	1,348,263		1,274,029
Residential Portfolio Segment \| Consumer mortgage
Loans receivable, net
Loans	3,629,301		3,617,186
Allowance for credit losses	(12,618)	$ (12,583)	(14,005)	(14,196)	$ (13,679)	$ (15,017)
Residential Portfolio Segment \| Home equity
Loans receivable, net
Loans	539,174		533,755
Allowance for credit losses	(1,600)	(1,512)	(1,590)	(1,483)	(1,394)	(1,548)
Consumer Portfolio Segment \| Consumer indirect
Loans receivable, net
Loans	1,871,343		1,859,354
Allowance for credit losses	(20,584)	(20,690)	(20,914)	(19,885)	(19,746)	(20,895)
Consumer Portfolio Segment \| Consumer direct
Loans receivable, net
Loans	202,387		205,595
Allowance for credit losses	$ (4,939)	$ (4,456)	$ (4,257)	$ (4,133)	$ (4,033)	$ (3,453)