ALLOWANCE FOR CREDIT LOSSES AND CREDIT QUALITY INFORMATION - Summary of Nonaccrual and Past Due Loans (Details) - USD ($)	Sep. 30, 2022	Dec. 31, 2021	Sep. 30, 2021
Financing Receivable, Past Due [Line Items]
Total Loans	$ 11,702,372,000	$ 7,882,055,000	$ 8,011,699,000
Nonaccrual Loans	$ 19,369,000	$ 16,609,000
Percent of nonaccrual loans	0.17%	0.21%
% of Total Loans	100.00%	100.00%
Nonaccrual with an allowance (less than)	$ 0	$ 100,000
Reverse mortgage, fair value	3,000,000	3,900,000	7,500,000
Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 56,776,000	$ 39,280,000
Percent past due	0.49%	0.50%
30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 32,022,000	$ 29,289,000
Percent past due	0.27%	0.37%
Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 24,754,000	$ 9,991,000
Percent past due	0.21%	0.13%
Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	$ 11,626,227,000	$ 7,826,166,000
Percent of accruing current balances	99.34%	99.29%
Residential
Financing Receivable, Past Due [Line Items]
Total Loans	$ 758,593,000	$ 542,733,000	574,681,000
Nonaccrual Loans	2,023,000	3,125,000
Residential | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	3,788,000	1,856,000
Residential | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	2,694,000	1,856,000
Residential | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	1,094,000	0
Residential | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	752,782,000	537,752,000
Consumer
Financing Receivable, Past Due [Line Items]
Total Loans	1,677,128,000	1,158,573,000	1,118,214,000
Nonaccrual Loans	1,952,000	2,380,000
Consumer | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	28,182,000	18,861,000
Consumer | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	14,873,000	10,227,000
Consumer | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	13,309,000	8,634,000
Consumer | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	1,646,994,000	1,137,332,000
Commercial and industrial | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	3,169,478,000	2,270,319,000	2,228,514,000
Nonaccrual Loans	4,837,000	8,211,000
Commercial and industrial | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	14,992,000	5,554,000
Commercial and industrial | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	6,641,000	5,007,000
Commercial and industrial | Commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	8,351,000	547,000
Commercial and industrial | Commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	3,149,649,000	2,256,554,000
Owner-occupied commercial | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	1,788,591,000	1,341,707,000	1,339,660,000
Nonaccrual Loans	339,000	811,000
Owner-occupied commercial | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	887,000	741,000
Owner-occupied commercial | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	887,000	741,000
Owner-occupied commercial | Commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	0	0
Owner-occupied commercial | Commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	1,787,365,000	1,340,155,000
Commercial mortgages | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	3,280,379,000	1,881,510,000	1,987,984,000
Nonaccrual Loans	5,060,000	2,070,000
Commercial mortgages | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	6,927,000	4,335,000
Commercial mortgages | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	6,927,000	3,525,000
Commercial mortgages | Commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	0	810,000
Commercial mortgages | Commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	3,268,392,000	1,875,105,000
Construction | Commercial
Financing Receivable, Past Due [Line Items]
Total Loans	1,028,203,000	687,213,000	$ 762,646,000
Nonaccrual Loans	5,158,000	12,000
Construction | Commercial | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	2,000,000	7,933,000
Construction | Commercial | 30–89 Days Past Due and Still  Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	0	7,933,000
Construction | Commercial | Greater  Than 90 Days Past Due and Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	2,000,000	0
Construction | Commercial | Accruing Current Balances
Financing Receivable, Past Due [Line Items]
Total Loans	1,021,045,000	679,268,000
Student loans | Consumer | Total Past Due And Still Accruing
Financing Receivable, Past Due [Line Items]
Total Loans	$ 23,800,000	$ 17,000,000