ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Summary of Nonaccrual and Past Due Loans (Details) - USD ($)	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 11,909,436,000	$ 7,882,055,000	$ 9,014,677,000
Nonaccrual Loans	$ 22,802,000	$ 16,609,000
Percent past due	0.40%	0.50%
Percent of accruing current balances	99.41%	99.29%
Percent of nonaccrual loans	0.19%	0.21%
% of Total Loans	100.00%	100.00%
Reverse mortgage, fair value	$ 2,400,000	$ 3,900,000	10,100,000
Nonaccrual with an allowance (prior year less than)	0	100,000
30–89 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 31,230,000	$ 29,289,000
Percent past due	0.26%	0.37%
Greater Than 90 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 16,535,000	$ 9,991,000
Percent past due	0.14%	0.13%
Total Past Due And Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 47,765,000	$ 39,280,000
Accruing Current Balances
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	11,838,869,000	7,826,166,000
Residential
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	759,465,000	542,733,000	764,393,000
Nonaccrual Loans	3,199,000	3,125,000
Residential | 30–89 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	2,563,000	1,856,000
Residential | Greater Than 90 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	0	0
Residential | Total Past Due And Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	2,563,000	1,856,000
Residential | Accruing Current Balances
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	753,703,000	537,752,000
Consumer
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,810,930,000	1,158,573,000	1,165,917,000
Nonaccrual Loans	2,145,000	2,380,000
Consumer | 30–89 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	12,263,000	10,227,000
Consumer | Greater Than 90 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	15,513,000	8,634,000
Consumer | Total Past Due And Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	27,776,000	18,861,000
Consumer | Accruing Current Balances
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,781,009,000	1,137,332,000
Commercial and industrial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,134,326,000	2,270,319,000	2,949,303,000
Nonaccrual Loans	6,770,000	8,211,000
Commercial and industrial | Commercial | 30–89 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	10,767,000	5,007,000
Commercial and industrial | Commercial | Greater Than 90 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	311,000	547,000
Commercial and industrial | Commercial | Total Past Due And Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	11,078,000	5,554,000
Commercial and industrial | Commercial | Accruing Current Balances
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,116,478,000	2,256,554,000
Owner-occupied commercial | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,809,582,000	1,341,707,000	1,332,727,000
Nonaccrual Loans	386,000	811,000
Owner-occupied commercial | Commercial | 30–89 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,500,000	741,000
Owner-occupied commercial | Commercial | Greater Than 90 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	474,000	0
Owner-occupied commercial | Commercial | Total Past Due And Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,974,000	741,000
Owner-occupied commercial | Commercial | Accruing Current Balances
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,805,222,000	1,340,155,000
Commercial mortgages | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,351,084,000	1,881,510,000	2,086,062,000
Nonaccrual Loans	5,159,000	2,070,000
Commercial mortgages | Commercial | 30–89 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	2,137,000	3,525,000
Commercial mortgages | Commercial | Greater Than 90 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	237,000	810,000
Commercial mortgages | Commercial | Total Past Due And Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	2,374,000	4,335,000
Commercial mortgages | Commercial | Accruing Current Balances
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	3,343,551,000	1,875,105,000
Construction | Commercial
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,044,049,000	687,213,000	$ 716,275,000
Nonaccrual Loans	5,143,000	12,000
Construction | Commercial | 30–89 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	0	7,933,000
Construction | Commercial | Greater Than 90 Days Past Due and Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	0	0
Construction | Commercial | Total Past Due And Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	0	7,933,000
Construction | Commercial | Accruing Current Balances
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	1,038,906,000	679,268,000
Student loans | Consumer | Total Past Due And Still Accruing
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total Loans	$ 21,100,000	$ 17,000,000