ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Schedule of Nonaccrual and Past Due Loans (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023	Sep. 30, 2023
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans With No Allowance	$ 66,195	$ 58,441
Nonaccrual Loans With An Allowance	23,844	5,568
Gross loans	$ 13,318,988	$ 12,766,518	$ 12,675,621
Percent of nonaccrual loans with no allowance	0.50%	0.46%
Percent of nonaccrual loans with an allowance	0.18%	0.04%
% of Total Loans	100.00%	100.00%
Reverse mortgage, fair value	$ 3,200	$ 2,800	2,800
Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 97,019	$ 47,397
Percent past due	0.73%	0.37%
30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 65,305	$ 35,813
Percent past due	0.49%	0.28%
Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 31,714	$ 11,584
Percent past due	0.24%	0.09%
Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	$ 13,131,930	$ 12,655,112
Percent of accruing current balances	98.59%	99.13%
Commercial | Commercial and industrial
Financing Receivable, Past Due [Line Items]
Total Loans	$ 2,639,266	$ 2,540,070
Nonaccrual Loans With No Allowance	41,095	13,645
Nonaccrual Loans With An Allowance	23,844	5,568
Gross loans	2,639,266	2,540,070	2,644,039
Commercial | Commercial and industrial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	3,042	1,923
Commercial | Commercial and industrial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	2,175	1,630
Commercial | Commercial and industrial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	867	293
Commercial | Commercial and industrial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	2,571,285	2,518,934
Commercial | Owner-occupied commercial
Financing Receivable, Past Due [Line Items]
Total Loans	2,003,722	1,886,087
Nonaccrual Loans With No Allowance	6,154	4,862
Nonaccrual Loans With An Allowance	0	0
Gross loans	2,003,722	1,886,087	1,924,171
Commercial | Owner-occupied commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	2,312	2,273
Commercial | Owner-occupied commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	1,719	1,786
Commercial | Owner-occupied commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	593	487
Commercial | Owner-occupied commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	1,995,256	1,878,952
Commercial | Commercial mortgages
Financing Receivable, Past Due [Line Items]
Total Loans	4,149,049	3,801,180
Nonaccrual Loans With No Allowance	7,449	22,292
Nonaccrual Loans With An Allowance	0	0
Gross loans	4,149,049	3,801,180	3,645,723
Commercial | Commercial mortgages | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	29,714	1,190
Commercial | Commercial mortgages | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	7,879	1,190
Commercial | Commercial mortgages | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	21,835	0
Commercial | Commercial mortgages | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	4,111,886	3,777,698
Commercial | Construction
Financing Receivable, Past Due [Line Items]
Total Loans	805,857	1,035,530
Nonaccrual Loans With No Allowance	3,308	12,617
Nonaccrual Loans With An Allowance	0	0
Gross loans	805,857	1,035,530	1,043,568
Commercial | Construction | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	22,979	0
Commercial | Construction | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	22,979	0
Commercial | Construction | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Commercial | Construction | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	779,570	1,022,913
Commercial | Commercial Small Business Leases
Financing Receivable, Past Due [Line Items]
Total Loans	645,421	623,622
Nonaccrual Loans With No Allowance	0	0
Nonaccrual Loans With An Allowance	0	0
Gross loans	645,421	623,622	605,698
Commercial | Commercial Small Business Leases | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	9,887	7,469
Commercial | Commercial Small Business Leases | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	9,237	6,697
Commercial | Commercial Small Business Leases | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	650	772
Commercial | Commercial Small Business Leases | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	635,534	616,153
Residential
Financing Receivable, Past Due [Line Items]
Total Loans	940,780	870,705
Nonaccrual Loans With No Allowance	5,099	2,579
Nonaccrual Loans With An Allowance	0	0
Gross loans	937,594	867,895	855,340
Residential | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	5,421	9,261
Residential | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	5,406	9,261
Residential | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	15	0
Residential | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	927,074	856,055
Consumer
Financing Receivable, Past Due [Line Items]
Total Loans	2,138,079	2,012,134
Nonaccrual Loans With No Allowance	3,090	2,446
Nonaccrual Loans With An Allowance	0	0
Gross loans	2,138,079	2,012,134	$ 1,957,082
Consumer | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	23,664	25,281
Consumer | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	15,910	15,249
Consumer | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	7,754	10,032
Consumer | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	2,111,325	1,984,407
Consumer | Student loans | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 14,200	$ 14,500