INVESTMENT SECURITIES - Schedule of Amortized Cost and Fair Value of Available-for-Sale Investment Securities Portfolio (Details) - USD ($) $ in Thousands	Sep. 30, 2026	Dec. 31, 2025
Available-for-Sale
Amortized Cost	$ 12,605,107	$ 12,059,997
Unrealized Gains	1,713	83,904
Unrealized Losses	(1,139,735)	(654,333)
Basis adjustments	(150,451)	(105,118)
Fair Value	11,316,634	11,384,450
U.S. Treasury
Available-for-Sale
Amortized Cost	257,667	269,313
Unrealized Gains	0	90
Unrealized Losses	(10,279)	(7,615)
Basis adjustments	(55,802)	(47,244)
Fair Value	191,586	214,544
U.S. government-sponsored entities and agencies
Available-for-Sale
Amortized Cost	1,562,644	1,567,036
Unrealized Gains	0	402
Unrealized Losses	(174,986)	(134,795)
Basis adjustments	(93,553)	(60,251)
Fair Value	1,294,105	1,372,392
Mortgage-backed securities - Agency
Available-for-Sale
Amortized Cost	10,329,298	9,575,241
Unrealized Gains	737	79,999
Unrealized Losses	(914,124)	(487,205)
Basis adjustments	0	0
Fair Value	9,415,911	9,168,035
States and political subdivisions
Available-for-Sale
Amortized Cost	290,742	438,642
Unrealized Gains	51	2,275
Unrealized Losses	(33,009)	(17,286)
Basis adjustments	(1,096)	2,377
Fair Value	256,688	426,008
Pooled trust preferred securities
Available-for-Sale
Amortized Cost	13,830	13,819
Unrealized Gains	0	0
Unrealized Losses	(843)	(2,085)
Basis adjustments	0	0
Fair Value	12,987	11,734
Other securities
Available-for-Sale
Amortized Cost	150,926	195,946
Unrealized Gains	925	1,138
Unrealized Losses	(6,494)	(5,347)
Basis adjustments	0	0
Fair Value	$ 145,357	$ 191,737

Debt Securities, Available-For-Sale, Accumulated Basis Adjustments, Before Tax

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Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
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-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481800/320-10-50-2

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 320
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Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
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