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LOANS AND ALLOWANCE FOR CREDIT LOSSES - Schedule of Composition of Loans and Impact of Adoption (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025	Dec. 31, 2025	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2024
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 50,772,584		$ 50,772,584		$ 48,764,162
Allowance for credit losses on loans	(580,511)	$ (565,109)	(580,511)	$ (565,109)	(569,520)	$ (574,358)	$ (401,932)	$ (392,522)
Net loans	50,192,073		50,192,073		48,194,642
Taxable	711,947	658,508	1,408,309	1,174,274
Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	0		0		0
Net loans	0		0		0
Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	50,772,584		50,772,584		48,764,162
Allowance for credit losses on loans	(580,511)		(580,511)		(569,520)
Net loans	50,192,073		50,192,073		48,194,642
Taxable			455,600		540,100
Commercial
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	16,112,685		16,112,685		14,983,861
Allowance for credit losses on loans	(253,854)	(215,917)	(253,854)	(215,917)	(244,670)	(244,640)	(157,587)	(148,722)
Commercial \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	(251,056)		(251,056)		(220,410)
Commercial \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	15,861,629		15,861,629		14,763,451
Commercial real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	22,535,229		22,535,229		22,050,007
Allowance for credit losses on loans	(263,706)	(294,303)	(263,706)	(294,303)	(268,332)	(266,797)	(198,110)	(200,309)
Commercial real estate \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	(185,429)		(185,429)		(175,670)
Commercial real estate \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	22,349,800		22,349,800		21,874,337
BBCC
Financing Receivable, Allowance for Credit Losses [Line Items]
Allowance for credit losses on loans	(2,961)	(2,488)	(2,961)	(2,488)	(2,371)	(2,779)	(2,695)	(2,813)
BBCC \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	436,485		436,485		396,080
BBCC \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	436,485		436,485		396,080
Residential real estate
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	8,760,832		8,760,832		8,467,496
Allowance for credit losses on loans	(40,450)	(31,850)	(40,450)	(31,850)	(34,394)	(39,764)	(24,214)	(22,922)
Residential real estate \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	0		0		0
Residential real estate \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	8,760,832		8,760,832		8,467,496
Consumer
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	3,363,838		3,363,838		3,262,798
Consumer \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	(3,363,838)		(3,363,838)		(3,262,798)
Indirect
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,183,585		1,183,585		1,075,235
Allowance for credit losses on loans	(7,228)	(8,430)	(7,228)	(8,430)	(8,021)	(8,309)	(9,063)	(8,434)
Indirect \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,183,585		1,183,585		1,075,235
Indirect \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,183,585		1,183,585		1,075,235
Direct
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	597,607		597,607		649,297
Allowance for credit losses on loans	(2,273)	(2,564)	(2,273)	(2,564)	(2,478)	(2,412)	(2,053)	(2,304)
Direct \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	597,607		597,607		649,297
Direct \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	597,607		597,607		649,297
Home equity
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,582,646		1,582,646		1,538,266
Allowance for credit losses on loans	(10,039)	$ (9,557)	(10,039)	$ (9,557)	(9,254)	$ (9,657)	$ (8,210)	$ (7,018)
Home equity \| Portfolio Segment Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,582,646		1,582,646		1,538,266
Home equity \| Portfolio Segment After Reclassifications
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	1,582,646		1,582,646		1,538,266
Direct Finance Leases
Financing Receivable, Allowance for Credit Losses [Line Items]
Total loans	$ 58,800		$ 58,800		$ 75,100