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LOANS AND ALLOWANCE FOR CREDIT LOSSES - Credit Quality By Past Due Status (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024
Aged analysis of the company's loans
Total Loans	$ 10,750,262	$ 10,432,365
Legacy Loan
Aged analysis of the company's loans
Total Loans	10,750,262	10,432,365
Nonaccrual	49,327	66,387
Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	51,605	55,946
Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	6,730	7,000
Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	107,662	129,333
Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	10,642,600	10,303,032
CRE - multifamily
Aged analysis of the company's loans
Total Loans	894,990	724,114
CRE - owner occupied
Aged analysis of the company's loans
Total Loans	860,399	864,783
CRE - non-owner occupied
Aged analysis of the company's loans
Total Loans	1,671,699	1,775,099
Commercial & industrial and other business loans
Aged analysis of the company's loans
Total Loans	1,236,790	1,141,182
Consumer mortgage
Aged analysis of the company's loans
Total Loans	3,544,277	3,489,780
Consumer indirect
Aged analysis of the company's loans
Total Loans	1,834,766	1,767,655
Consumer direct
Aged analysis of the company's loans
Total Loans	196,408	192,327
Consumer direct | Legacy Loan
Aged analysis of the company's loans
Total Loans		192,327
Nonaccrual		0
Consumer direct | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans		1,747
Consumer direct | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans		106
Consumer direct | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans		1,853
Consumer direct | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans		190,474
Home equity
Aged analysis of the company's loans
Total Loans	510,933	477,425
Business lending
Aged analysis of the company's loans
Total Loans	4,663,878	4,505,178
Business lending | Loans under 250,000
Aged analysis of the company's loans
Business lending loans	250,000
Business lending | Loans from 250,000 to 2 million
Aged analysis of the company's loans
Business lending loans	2,000
Business lending | Loans 2 million to 3 million range
Aged analysis of the company's loans
Business lending loans	3,000
Business lending | Loans greater than 3 million
Aged analysis of the company's loans
Business lending loans	3,000
Commercial Portfolio Segment | CRE - multifamily
Aged analysis of the company's loans
Total Loans	894,990	724,114
Commercial Portfolio Segment | CRE - multifamily | Legacy Loan
Aged analysis of the company's loans
Total Loans	894,990	724,114
Nonaccrual	0	12,316
Commercial Portfolio Segment | CRE - multifamily | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	1,060	184
Commercial Portfolio Segment | CRE - multifamily | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	0	0
Commercial Portfolio Segment | CRE - multifamily | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	1,060	12,500
Commercial Portfolio Segment | CRE - multifamily | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	893,930	711,614
Commercial Portfolio Segment | CRE - owner occupied
Aged analysis of the company's loans
Total Loans	860,399	864,783
Commercial Portfolio Segment | CRE - owner occupied | Legacy Loan
Aged analysis of the company's loans
Total Loans	860,399	864,783
Nonaccrual	6,699	7,695
Commercial Portfolio Segment | CRE - owner occupied | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	240	690
Commercial Portfolio Segment | CRE - owner occupied | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	475	0
Commercial Portfolio Segment | CRE - owner occupied | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	7,414	8,385
Commercial Portfolio Segment | CRE - owner occupied | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	852,985	856,398
Commercial Portfolio Segment | CRE - non-owner occupied
Aged analysis of the company's loans
Total Loans	1,671,699	1,775,099
Commercial Portfolio Segment | CRE - non-owner occupied | Legacy Loan
Aged analysis of the company's loans
Total Loans	1,671,699	1,775,099
Nonaccrual	1,422	11,826
Commercial Portfolio Segment | CRE - non-owner occupied | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	264	447
Commercial Portfolio Segment | CRE - non-owner occupied | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	0	0
Commercial Portfolio Segment | CRE - non-owner occupied | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	1,686	12,273
Commercial Portfolio Segment | CRE - non-owner occupied | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	1,670,013	1,762,826
Commercial Portfolio Segment | Commercial & industrial and other business loans
Aged analysis of the company's loans
Total Loans	1,236,790	1,141,182
Commercial Portfolio Segment | Commercial & industrial and other business loans | Legacy Loan
Aged analysis of the company's loans
Total Loans	1,236,790	1,141,182
Nonaccrual	12,937	8,122
Commercial Portfolio Segment | Commercial & industrial and other business loans | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	618	2,832
Commercial Portfolio Segment | Commercial & industrial and other business loans | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	0	0
Commercial Portfolio Segment | Commercial & industrial and other business loans | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	13,555	10,954
Commercial Portfolio Segment | Commercial & industrial and other business loans | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	1,223,235	1,130,228
Residential Portfolio Segment | Consumer mortgage
Aged analysis of the company's loans
Total Loans	3,544,277	3,489,780
Residential Portfolio Segment | Consumer mortgage | Legacy Loan
Aged analysis of the company's loans
Total Loans	3,544,277	3,489,780
Nonaccrual	26,377	24,389
Residential Portfolio Segment | Consumer mortgage | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	23,748	24,928
Residential Portfolio Segment | Consumer mortgage | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	4,899	5,288
Residential Portfolio Segment | Consumer mortgage | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	55,024	54,605
Residential Portfolio Segment | Consumer mortgage | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	3,489,253	3,435,175
Residential Portfolio Segment | Home equity
Aged analysis of the company's loans
Total Loans	510,933	477,425
Residential Portfolio Segment | Home equity | Legacy Loan
Aged analysis of the company's loans
Total Loans	510,933	477,425
Nonaccrual	1,892	2,039
Residential Portfolio Segment | Home equity | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	3,152	2,739
Residential Portfolio Segment | Home equity | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	372	379
Residential Portfolio Segment | Home equity | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	5,416	5,157
Residential Portfolio Segment | Home equity | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	505,517	472,268
Consumer Portfolio Segment | Consumer indirect
Aged analysis of the company's loans
Total Loans	1,834,766	1,767,655
Consumer Portfolio Segment | Consumer indirect | Legacy Loan
Aged analysis of the company's loans
Total Loans	1,834,766	1,767,655
Nonaccrual	0	0
Consumer Portfolio Segment | Consumer indirect | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	20,885	22,379
Consumer Portfolio Segment | Consumer indirect | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	810	1,227
Consumer Portfolio Segment | Consumer indirect | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	21,695	23,606
Consumer Portfolio Segment | Consumer indirect | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	1,813,071	1,744,049
Consumer Portfolio Segment | Consumer direct
Aged analysis of the company's loans
Total Loans	196,408	$ 192,327
Consumer Portfolio Segment | Consumer direct | Legacy Loan
Aged analysis of the company's loans
Total Loans	196,408
Nonaccrual	0
Consumer Portfolio Segment | Consumer direct | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	1,638
Consumer Portfolio Segment | Consumer direct | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	174
Consumer Portfolio Segment | Consumer direct | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	1,812
Consumer Portfolio Segment | Consumer direct | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	$ 194,596

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