INVESTMENT SECURITIES - Summary of Amortized Cost, Gross Unrealized Gains and Losses and Approximate Fair Value of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2026	Dec. 31, 2025
Available for sale securities
Amortized Cost	$ 1,542,274	$ 1,574,023
Gross Unrealized Gains	18	1,826
Gross Unrealized Losses	(290,752)	(168,747)
Fair Value	1,251,540	1,407,102
Held to maturity securities
Amortized Cost	1,873,196	1,971,784
Allowance for Credit Losses	(245)	(245)
Net Carrying Amount	1,872,951	1,971,539
Gross Unrealized Gains	2	868
Gross Unrealized Losses	(377,721)	(254,365)
Fair Value	1,495,477	1,718,287
U.S. Government-sponsored agency securities
Available for sale securities
Amortized Cost	81,543	87,936
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(14,347)	(11,837)
Fair Value	67,196	76,099
Held to maturity securities
Amortized Cost	308,998	324,643
Allowance for Credit Losses	0	0
Net Carrying Amount	308,998	324,643
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(52,277)	(46,693)
Fair Value	256,721	277,950
State and municipal
Available for sale securities
Amortized Cost	982,812	993,911
Gross Unrealized Gains	0	225
Gross Unrealized Losses	(192,870)	(91,842)
Fair Value	789,942	902,294
Held to maturity securities
Amortized Cost	1,043,391	1,069,653
Allowance for Credit Losses	(245)	(245)
Net Carrying Amount	1,043,146	1,069,408
Gross Unrealized Gains	2	868
Gross Unrealized Losses	(237,783)	(137,706)
Fair Value	805,610	932,815
U.S. Government-sponsored mortgage-backed securities
Available for sale securities
Amortized Cost	469,402	482,702
Gross Unrealized Gains	7	1,600
Gross Unrealized Losses	(83,370)	(64,792)
Fair Value	386,039	419,510
Held to maturity securities
Amortized Cost	520,807	577,488
Allowance for Credit Losses	0	0
Net Carrying Amount	520,807	577,488
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(87,661)	(69,966)
Fair Value	433,146	507,522
Foreign investment
Available for sale securities
Amortized Cost	1,500	1,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(9)	0
Fair Value	1,491	1,500
Corporate obligations
Available for sale securities
Amortized Cost	7,017	7,974
Gross Unrealized Gains	11	1
Gross Unrealized Losses	(156)	(276)
Fair Value	$ 6,872	$ 7,699

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).

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