ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Summary of Nonaccrual and Past Due Loans (Details) - USD ($)	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Financing Receivable, Past Due [Line Items]
Nonaccrual Loans With No Allowance	$ 20,742,000	$ 22,802,000
Nonaccrual Loans With An Allowance	12,261,000	0
Gross loans	$ 12,336,834,000	$ 11,909,436,000	$ 11,480,118,000
Percent of nonaccrual loans with no allowance	0.17%	0.19%
Percent of nonaccrual loans with allowance	0.10%
% of Total Loans	100.00%	100.00%
Reverse mortgage, fair value	$ 3,100,000	$ 2,400,000	2,600,000
Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 48,758,000	$ 47,765,000
Percent past due	0.40%	0.40%
30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 35,187,000	$ 31,230,000
Percent past due	0.29%	0.26%
Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 13,571,000	$ 16,535,000
Percent past due	0.11%	0.14%
Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	$ 12,255,073,000	$ 11,838,869,000
Percent of accruing current balances	99.33%	99.41%
Residential
Financing Receivable, Past Due [Line Items]
Total Loans	$ 829,832,000	$ 761,882,000
Nonaccrual Loans With No Allowance	2,709,000	3,199,000
Nonaccrual Loans With An Allowance	0
Gross loans	826,750,000	759,465,000	770,575,000
Residential | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	3,176,000	2,563,000
Residential | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	3,176,000	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	820,865,000	753,703,000
Consumer
Financing Receivable, Past Due [Line Items]
Total Loans	1,905,219,000	1,810,930,000
Nonaccrual Loans With No Allowance	2,308,000	2,145,000
Nonaccrual Loans With An Allowance	0
Gross loans	1,905,219,000	1,810,930,000	1,522,596,000
Consumer | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	26,484,000	27,776,000
Consumer | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	14,255,000	12,263,000
Consumer | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	12,229,000	15,513,000
Consumer | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	1,876,427,000	1,781,009,000
Commercial and industrial | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	2,623,723,000	2,575,345,000
Nonaccrual Loans With No Allowance	6,017,000	6,770,000
Nonaccrual Loans With An Allowance	12,261,000
Gross loans	3,213,786,000	3,134,326,000	3,107,740,000
Commercial and industrial | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	9,309,000	11,078,000
Commercial and industrial | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	8,320,000	10,767,000
Commercial and industrial | Commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	989,000	311,000
Commercial and industrial | Commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	3,186,199,000	3,116,478,000
Owner-occupied commercial | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	1,883,055,000	1,809,582,000
Nonaccrual Loans With No Allowance	2,664,000	386,000
Nonaccrual Loans With An Allowance	0
Gross loans	1,883,055,000	1,809,582,000	1,823,229,000
Owner-occupied commercial | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	2,350,000	3,974,000
Owner-occupied commercial | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	2,350,000	3,500,000
Owner-occupied commercial | Commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	0	474,000
Owner-occupied commercial | Commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	1,878,041,000	1,805,222,000
Commercial mortgages | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	3,552,800,000	3,351,084,000
Nonaccrual Loans With No Allowance	6,303,000	5,159,000
Nonaccrual Loans With An Allowance	0
Gross loans	3,552,800,000	3,351,084,000	3,321,654,000
Commercial mortgages | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	5,388,000	2,374,000
Commercial mortgages | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	5,035,000	2,137,000
Commercial mortgages | Commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	353,000	237,000
Commercial mortgages | Commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	3,541,109,000	3,343,551,000
Construction | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	955,224,000	1,044,049,000
Nonaccrual Loans With No Allowance	741,000	5,143,000
Nonaccrual Loans With An Allowance	0
Gross loans	955,224,000	1,044,049,000	$ 934,324,000
Construction | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	2,051,000	0
Construction | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	2,051,000	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	952,432,000	1,038,906,000
Student loans | Consumer | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 18,200,000	$ 21,100,000