LOANS AND ALLOWANCE FOR CREDIT LOSSES - Credit Quality By Past Due Status (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Aged analysis of the company's loans
Total Loans	$ 9,883,500		$ 9,704,598
Interest income on nonaccrual loans	0	$ 0
Legacy Loan
Aged analysis of the company's loans
Total Loans	9,883,500		9,704,598
Nonaccrual	44,904		48,687
Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	42,131		48,442
Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	4,554		5,886
Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	91,589		103,015
Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	9,791,911		9,601,583
CRE - multifamily
Aged analysis of the company's loans
Total Loans	658,278		619,794
CRE - owner occupied
Aged analysis of the company's loans
Total Loans	777,302		752,774
CRE - non-owner occupied
Aged analysis of the company's loans
Total Loans	1,750,038		1,711,198
Nonaccrual	13,368
CRE - non-owner occupied | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	247
CRE - non-owner occupied | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	0
CRE - non-owner occupied | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	13,615
CRE - non-owner occupied | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	1,736,423
Commercial & industrial and other business loans
Aged analysis of the company's loans
Total Loans	1,034,581		1,000,630
Nonaccrual	647
Commercial & industrial and other business loans | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	1,402
Commercial & industrial and other business loans | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	0
Commercial & industrial and other business loans | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	2,049
Commercial & industrial and other business loans | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	1,032,532
Business lending
Aged analysis of the company's loans
Total Loans	4,220,199		4,084,396
Consumer mortgage
Aged analysis of the company's loans
Total Loans	3,317,467		3,285,018
Nonaccrual	27,066
Consumer mortgage | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	17,265
Consumer mortgage | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	3,115
Consumer mortgage | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	47,446
Consumer mortgage | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	3,270,021
Consumer indirect
Aged analysis of the company's loans
Total Loans	1,716,028		1,703,440
Consumer direct
Aged analysis of the company's loans
Total Loans	183,750		185,229
Home equity
Aged analysis of the company's loans
Total Loans	446,056		446,515
Commercial Portfolio Segment | CRE - multifamily
Aged analysis of the company's loans
Total Loans	658,278		619,794
Commercial Portfolio Segment | CRE - multifamily | Legacy Loan
Aged analysis of the company's loans
Total Loans	658,278
Nonaccrual	0
Commercial Portfolio Segment | CRE - multifamily | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	0
Commercial Portfolio Segment | CRE - multifamily | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	0
Commercial Portfolio Segment | CRE - multifamily | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	0
Commercial Portfolio Segment | CRE - multifamily | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	658,278
Commercial Portfolio Segment | CRE - owner occupied
Aged analysis of the company's loans
Total Loans	777,302		752,774
Commercial Portfolio Segment | CRE - non-owner occupied
Aged analysis of the company's loans
Total Loans	1,750,038		1,711,198
Commercial Portfolio Segment | Commercial & industrial and other business loans
Aged analysis of the company's loans
Total Loans	1,034,581		1,000,630
Commercial Portfolio Segment | Business lending | Legacy Loan
Aged analysis of the company's loans
Total Loans			619,794
Nonaccrual			0
Commercial Portfolio Segment | Business lending | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans			0
Commercial Portfolio Segment | Business lending | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans			0
Commercial Portfolio Segment | Business lending | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans			0
Commercial Portfolio Segment | Business lending | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans			619,794
Residential Portfolio Segment | CRE - owner occupied | Legacy Loan
Aged analysis of the company's loans
Total Loans	777,302		752,774
Nonaccrual	1,536		1,953
Residential Portfolio Segment | CRE - owner occupied | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	1,602		1,477
Residential Portfolio Segment | CRE - owner occupied | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	0		0
Residential Portfolio Segment | CRE - owner occupied | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	3,138		3,430
Residential Portfolio Segment | CRE - owner occupied | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	774,164		749,344
Residential Portfolio Segment | Consumer mortgage
Aged analysis of the company's loans
Total Loans	3,317,467		3,285,018
Residential Portfolio Segment | Consumer mortgage | Legacy Loan
Aged analysis of the company's loans
Total Loans			3,285,018
Nonaccrual			26,043
Residential Portfolio Segment | Consumer mortgage | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans			18,434
Residential Portfolio Segment | Consumer mortgage | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans			4,559
Residential Portfolio Segment | Consumer mortgage | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans			49,036
Residential Portfolio Segment | Consumer mortgage | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans			3,235,982
Residential Portfolio Segment | Home equity | Legacy Loan
Aged analysis of the company's loans
Total Loans	446,056		446,515
Nonaccrual	2,266		2,368
Residential Portfolio Segment | Home equity | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	3,848		3,546
Residential Portfolio Segment | Home equity | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	502		416
Residential Portfolio Segment | Home equity | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	6,616		6,330
Residential Portfolio Segment | Home equity | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	439,440		440,185
Consumer Portfolio Segment | CRE - non-owner occupied | Legacy Loan
Aged analysis of the company's loans
Total Loans			1,711,198
Nonaccrual			17,964
Consumer Portfolio Segment | CRE - non-owner occupied | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans			2,311
Consumer 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
Consumer Portfolio Segment | CRE - non-owner occupied | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans			20,275
Consumer Portfolio Segment | CRE - non-owner occupied | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans			1,690,923
Consumer Portfolio Segment | Commercial & industrial and other business loans | Legacy Loan
Aged analysis of the company's loans
Total Loans			1,000,630
Nonaccrual			336
Consumer Portfolio Segment | Commercial & industrial and other business loans | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans			880
Consumer 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
Consumer Portfolio Segment | Commercial & industrial and other business loans | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans			1,216
Consumer Portfolio Segment | Commercial & industrial and other business loans | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans			999,414
Consumer Portfolio Segment | Consumer indirect
Aged analysis of the company's loans
Total Loans	1,716,028		1,703,440
Consumer Portfolio Segment | Consumer indirect | Legacy Loan
Aged analysis of the company's loans
Total Loans	1,716,028		1,703,440
Nonaccrual	0		0
Consumer Portfolio Segment | Consumer indirect | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	16,604		20,215
Consumer Portfolio Segment | Consumer indirect | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	865		776
Consumer Portfolio Segment | Consumer indirect | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	17,469		20,991
Consumer Portfolio Segment | Consumer indirect | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	1,698,559		1,682,449
Consumer Portfolio Segment | Consumer direct
Aged analysis of the company's loans
Total Loans	183,750		185,229
Consumer Portfolio Segment | Consumer direct | Legacy Loan
Aged analysis of the company's loans
Total Loans	183,750		185,229
Nonaccrual	21		23
Consumer Portfolio Segment | Consumer direct | Legacy Loan | Past Due 30 - 89 Days
Aged analysis of the company's loans
Total Loans	1,163		1,579
Consumer Portfolio Segment | Consumer direct | Legacy Loan | 90+ Days Past Due and Still Accruing
Aged analysis of the company's loans
Total Loans	72		135
Consumer Portfolio Segment | Consumer direct | Legacy Loan | Financial Asset, Past Due
Aged analysis of the company's loans
Total Loans	1,256		1,737
Consumer Portfolio Segment | Consumer direct | Legacy Loan | Financial Asset, Not Past Due
Aged analysis of the company's loans
Total Loans	182,494		183,492
Consumer Portfolio Segment | Home equity
Aged analysis of the company's loans
Total Loans	$ 446,056		$ 446,515