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ALLOWANCE FOR CREDIT LOSSES FOR LOANS AND FINANCE LEASES - Carrying Amount of Portfolios (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Dec. 31, 2024
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 13,091,077	$ 13,125,356
Allowance for credit losses	245,060	249,037	$ 247,269	$ 243,942
Residential Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	2,914,898	2,908,302
Allowance for credit losses	$ 41,534	$ 41,071	41,640	40,654
Residential Mortgage Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	1.42%	1.41%
Commercial Portfolio Segment [Member] \| Construction Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 195,267	$ 265,568
Allowance for credit losses	$ 3,324	$ 5,672	3,417	3,824
Commercial Portfolio Segment [Member] \| Construction Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	1.70%	2.14%
Commercial Portfolio Segment [Member] \| Commercial Mortgage Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 2,627,113	$ 2,554,252
Allowance for credit losses	$ 23,670	$ 23,832	24,143	22,447
Commercial Portfolio Segment [Member] \| Commercial Mortgage Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	0.90%	0.93%
Commercial Portfolio Segment [Member] \| Commercial and Industrial Loans [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 3,694,843	$ 3,688,358
Allowance for credit losses	$ 42,124	$ 41,416	36,464	33,034
Commercial Portfolio Segment [Member] \| Commercial and Industrial Loans [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	1.14%	1.12%
Consumer Portfolio Segment [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Amortized cost of loans	$ 3,658,956	$ 3,708,876
Allowance for credit losses	$ 134,408	$ 137,046	$ 141,605	$ 143,983
Consumer Portfolio Segment [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	3.67%	3.70%
Loan Total [Member] \| Allowance for loan and lease losses, numerator [Member] \| Loans Receivable [Member]
Financing Receivable Allowance For Credit Losses [Line Items]
Allowance for credit losses to amortized cost	1.87%	1.90%