ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Summary of Nonaccrual and Past Due Loans (Details) - USD ($)	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans With No Allowance	$ 15,101,000	$ 22,802,000
Nonaccrual Loans With An Allowance	16,916,000	0
Gross loans	$ 12,143,268,000	$ 11,909,436,000	$ 11,329,528,000
Percent of nonaccrual loans with no allowance	0.12%	0.19%
Percent of nonaccrual loans with allowance	0.14%
% of Total Loans	100.00%	100.00%
Reverse mortgage, fair value	$ 2,700,000	$ 2,400,000	4,300,000
Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 80,333,000	$ 47,765,000
Percent past due	0.66%	0.40%
30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 66,768,000	$ 31,230,000
Percent past due	0.55%	0.26%
Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 13,565,000	$ 16,535,000
Percent past due	0.11%	0.14%
Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	$ 12,030,918,000	$ 11,838,869,000
Percent of accruing current balances	99.08%	99.41%
Residential
Financing Receivable, Past Due [Line Items]
Total Loans	$ 788,799,000	$ 761,882,000
Nonaccrual Loans With No Allowance	2,064,000	3,199,000
Nonaccrual Loans With An Allowance	0
Gross loans	786,060,000	759,465,000	805,326,000
Residential | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	4,136,000	2,563,000
Residential | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	4,136,000	2,563,000
Residential | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Residential | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	779,860,000	753,703,000
Consumer
Financing Receivable, Past Due [Line Items]
Total Loans	1,868,427,000	1,810,930,000
Nonaccrual Loans With No Allowance	2,018,000	2,145,000
Nonaccrual Loans With An Allowance	0
Gross loans	1,868,427,000	1,810,930,000	1,382,116,000
Consumer | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	23,020,000	27,776,000
Consumer | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	11,361,000	12,263,000
Consumer | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	11,659,000	15,513,000
Consumer | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	1,843,389,000	1,781,009,000
Commercial and industrial | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	2,568,742,000	2,575,345,000
Nonaccrual Loans With No Allowance	3,749,000	6,770,000
Nonaccrual Loans With An Allowance	16,712,000
Gross loans	3,145,326,000	3,134,326,000	2,984,127,000
Commercial and industrial | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	32,341,000	11,078,000
Commercial and industrial | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	31,426,000	10,767,000
Commercial and industrial | Commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	915,000	311,000
Commercial and industrial | Commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	3,092,524,000	3,116,478,000
Owner-occupied commercial | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	1,846,661,000	1,809,582,000
Nonaccrual Loans With No Allowance	377,000	386,000
Nonaccrual Loans With An Allowance	204,000
Gross loans	1,846,661,000	1,809,582,000	1,872,827,000
Owner-occupied commercial | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	5,630,000	3,974,000
Owner-occupied commercial | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	5,326,000	3,500,000
Owner-occupied commercial | Commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	304,000	474,000
Owner-occupied commercial | Commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	1,840,450,000	1,805,222,000
Commercial mortgages | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	3,473,083,000	3,351,084,000
Nonaccrual Loans With No Allowance	6,133,000	5,159,000
Nonaccrual Loans With An Allowance	0
Gross loans	3,473,083,000	3,351,084,000	3,361,242,000
Commercial mortgages | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	8,874,000	2,374,000
Commercial mortgages | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	8,187,000	2,137,000
Commercial mortgages | Commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	687,000	237,000
Commercial mortgages | Commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	3,458,076,000	3,343,551,000
Construction | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	1,023,711,000	1,044,049,000
Nonaccrual Loans With No Allowance	760,000	5,143,000
Nonaccrual Loans With An Allowance	0
Gross loans	1,023,711,000	1,044,049,000	$ 923,890,000
Construction | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	6,332,000	0
Construction | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	6,332,000	0
Construction | Commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Construction | Commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	1,016,619,000	1,038,906,000
Student loans | Consumer | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 15,500,000	$ 21,100,000