INVESTMENT SECURITIES - Amortized Cost and Approximate Fair Value of Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Available for sale securities
Amortized Cost	$ 1,867,872	$ 1,846,840
Gross Unrealized Gains	363	826
Gross Unrealized Losses	248,022	220,554
Fair Value	1,620,213	1,627,112
Held to maturity securities
Amortized Cost	2,163,606	2,184,497
Allowance for Credit Losses	245	245
Net Carrying Amount	2,163,361	2,184,252
Gross Unrealized Gains	691	1,625
Gross Unrealized Losses	343,846	315,748
Fair Value	1,820,451	1,870,374
U.S. Government-sponsored agency securities
Available for sale securities
Amortized Cost	110,457	111,521
Gross Unrealized Gains	0	0
Gross Unrealized Losses	17,325	16,214
Fair Value	93,132	95,307
Held to maturity securities
Amortized Cost	370,310	374,002
Allowance for Credit Losses	0	0
Net Carrying Amount	370,310	374,002
Gross Unrealized Gains	0	0
Gross Unrealized Losses	66,154	64,159
Fair Value	304,156	309,843
State and municipal
Available for sale securities
Amortized Cost	1,179,288	1,181,029
Gross Unrealized Gains	27	364
Gross Unrealized Losses	136,252	116,222
Fair Value	1,043,063	1,065,171
Held to maturity securities
Amortized Cost	1,097,848	1,099,201
Allowance for Credit Losses	245	245
Net Carrying Amount	1,097,603	1,098,956
Gross Unrealized Gains	691	1,625
Gross Unrealized Losses	171,353	152,113
Fair Value	927,186	948,713
U.S. Government-sponsored mortgage-backed securities
Available for sale securities
Amortized Cost	565,177	541,343
Gross Unrealized Gains	336	462
Gross Unrealized Losses	93,469	86,990
Fair Value	472,044	454,815
Held to maturity securities
Amortized Cost	693,948	709,794
Allowance for Credit Losses	0	0
Net Carrying Amount	693,948	709,794
Gross Unrealized Gains	0	0
Gross Unrealized Losses	106,317	99,448
Fair Value	587,631	610,346
Corporate obligations
Available for sale securities
Amortized Cost	12,950	12,947
Gross Unrealized Gains	0	0
Gross Unrealized Losses	976	1,128
Fair Value	11,974	11,819
Foreign investment
Held to maturity securities
Amortized Cost	1,500	1,500
Allowance for Credit Losses	0	0
Net Carrying Amount	1,500	1,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses	22	28
Fair Value	$ 1,478	$ 1,472

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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