ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Schedule of Nonaccrual and Past Due Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Dec. 31, 2024	Sep. 30, 2024
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans With No Allowance	$ 35,042	$ 103,578
Nonaccrual Loans With An Allowance	26,760	18,603
Total Loans	$ 12,955,253	$ 13,187,874	$ 13,318,988
Percent of nonaccrual loans with no allowance	0.27%	0.79%
Percent of nonaccrual loans with an allowance	0.21%	0.14%
% of Total Loans	100.00%	100.00%
Reverse mortgage, fair value	$ 5,300	$ 3,600	3,200
Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	$ 49,805	$ 44,768
Percent past due	0.38%	0.34%
30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	$ 35,510	$ 35,566
Percent past due	0.27%	0.27%
Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	$ 14,295	$ 9,202
Percent past due	0.11%	0.07%
Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Gross loans	$ 12,843,646	$ 13,020,925
Percent of accruing current balances	99.14%	98.73%
Commercial | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Gross loans	$ 2,625,152	$ 2,656,174
Nonaccrual Loans With No Allowance	14,842	43,206
Nonaccrual Loans With An Allowance	0	18,603
Total Loans	2,625,152	2,656,174	2,639,266
Commercial | Commercial and industrial | Discontinued Operations, Held-for-Sale
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans With No Allowance	10,300
Commercial | Commercial and industrial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	4,421	1,970
Commercial | Commercial and industrial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	3,252	1,482
Commercial | Commercial and industrial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	1,169	488
Commercial | Commercial and industrial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Gross loans	2,605,889	2,592,395
Commercial | Owner-occupied commercial
Financing Receivable, Past Due [Line Items]
Gross loans	1,922,767	1,973,645
Nonaccrual Loans With No Allowance	6,502	4,710
Nonaccrual Loans With An Allowance	0	0
Total Loans	1,922,767	1,973,645	2,003,722
Commercial | Owner-occupied commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	4,452	902
Commercial | Owner-occupied commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	4,065	706
Commercial | Owner-occupied commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	387	196
Commercial | Owner-occupied commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Gross loans	1,911,813	1,968,033
Commercial | Commercial mortgages
Financing Receivable, Past Due [Line Items]
Gross loans	3,855,971	4,030,627
Nonaccrual Loans With No Allowance	3,145	22,223
Nonaccrual Loans With An Allowance	0	0
Total Loans	3,855,971	4,030,627	4,149,049
Commercial | Commercial mortgages | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	9,063	3,183
Commercial | Commercial mortgages | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	7,477	2,621
Commercial | Commercial mortgages | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	1,586	562
Commercial | Commercial mortgages | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Gross loans	3,843,763	4,005,221
Commercial | Construction
Financing Receivable, Past Due [Line Items]
Gross loans	1,003,986	832,093
Nonaccrual Loans With No Allowance	2,621	25,600
Nonaccrual Loans With An Allowance	26,760	0
Total Loans	1,003,986	832,093	805,857
Commercial | Construction | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	0	0
Commercial | Construction | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	0	0
Commercial | Construction | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	0	0
Commercial | Construction | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Gross loans	974,605	806,493
Commercial | Commercial Small Business Leases
Financing Receivable, Past Due [Line Items]
Gross loans	617,256	647,516
Nonaccrual Loans With No Allowance	0	0
Nonaccrual Loans With An Allowance	0	0
Total Loans	617,256	647,516	645,421
Commercial | Commercial Small Business Leases | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	7,876	8,975
Commercial | Commercial Small Business Leases | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	7,122	8,409
Commercial | Commercial Small Business Leases | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	754	566
Commercial | Commercial Small Business Leases | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Gross loans	609,380	638,541
Residential
Financing Receivable, Past Due [Line Items]
Gross loans	1,038,656	965,051
Nonaccrual Loans With No Allowance	4,892	5,011
Nonaccrual Loans With An Allowance	0	0
Total Loans	1,033,343	961,426	937,594
Residential | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	4,722	4,277
Residential | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	4,533	4,262
Residential | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	189	15
Residential | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Gross loans	1,023,729	952,138
Consumer
Financing Receivable, Past Due [Line Items]
Gross loans	1,896,778	2,086,393
Nonaccrual Loans With No Allowance	3,040	2,828
Nonaccrual Loans With An Allowance	0	0
Total Loans	1,896,778	2,086,393	$ 2,138,079
Consumer | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	19,271	25,461
Consumer | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	9,061	18,086
Consumer | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	10,210	7,375
Consumer | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Gross loans	1,874,467	2,058,104
Consumer | Student loans | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Gross loans	$ 15,200	$ 15,600