INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Available-for-Sale and Held-to-Maturity Investment Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Available-for-Sale Debt Securities
Amortized Cost	$ 4,218,266	$ 4,504,342
Gross Unrealized Gain	285	168
Gross Unrealized Loss	707,903	657,973
Allowance for Credit Losses	0	0
Fair Value	3,510,648	3,846,537
Held-to-Maturity Debt Securities
Amortized Cost	1,015,168	1,058,565
Gross Unrealized Gain	247	2,665
Gross Unrealized Loss	119,897	75,291
Allowance for Credit Losses	7	8
Fair Value	895,511	985,931
Available for sale securities transfers to held to maturity unrealized losses	100,500	120,400
Collateralized mortgage obligations (CMO)
Available-for-Sale Debt Securities
Amortized Cost	526,796	560,952
Gross Unrealized Gain	113	0
Gross Unrealized Loss	95,967	96,333
Allowance for Credit Losses	0	0
Fair Value	430,942	464,619
Fannie Mae (FNMA) mortgage-backed securities (MBS)
Available-for-Sale Debt Securities
Amortized Cost	3,305,418	3,544,762
Gross Unrealized Gain	172	162
Gross Unrealized Loss	550,011	502,574
Allowance for Credit Losses	0	0
Fair Value	2,755,579	3,042,350
Held-to-Maturity Debt Securities
Amortized Cost	831,325	872,653
Gross Unrealized Gain	0	0
Gross Unrealized Loss	116,600	74,332
Allowance for Credit Losses	0	0
Fair Value	714,725	798,321
Freddie Mac (FHLMC) MBS
Available-for-Sale Debt Securities
Amortized Cost	118,605	126,856
Gross Unrealized Gain	0	0
Gross Unrealized Loss	13,091	11,324
Allowance for Credit Losses	0	0
Fair Value	105,514	115,532
Ginnie Mae (GNMA) MBS
Available-for-Sale Debt Securities
Amortized Cost	44,578	46,333
Gross Unrealized Gain	0	6
Gross Unrealized Loss	3,902	2,999
Allowance for Credit Losses	0	0
Fair Value	40,676	43,340
Government-sponsored enterprises (GSE) agency notes
Available-for-Sale Debt Securities
Amortized Cost	222,869	225,439
Gross Unrealized Gain	0	0
Gross Unrealized Loss	44,932	44,743
Allowance for Credit Losses	0	0
Fair Value	177,937	180,696
State and political subdivisions
Held-to-Maturity Debt Securities
Amortized Cost	183,843	185,912
Gross Unrealized Gain	247	2,665
Gross Unrealized Loss	3,297	959
Allowance for Credit Losses	7	8	$ 10	$ 4
Fair Value	$ 180,786	$ 187,610

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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