INVESTMENT SECURITIES - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale and Held-to-Maturity Investment Securities (Details) - USD ($)	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Available-for-Sale Debt Securities
Amortized Cost	$ 4,163,541,000	$ 4,218,266,000
Gross Unrealized Gain	1,247,000	285,000
Gross Unrealized Loss	616,711,000	707,903,000
Allowance for Credit Losses	0	0
Fair Value	3,548,077,000	3,510,648,000
Held-to-Maturity Debt Securities
Amortized Cost	1,006,416,000	1,015,168,000
Gross Unrealized Gain	57,000	247,000
Gross Unrealized Loss	107,728,000	119,897,000
Beginning balance	6,000	7,000	$ 8,000	$ 8,000
Fair Value	898,739,000	895,511,000
Available for sale securities transfers to held to maturity unrealized losses	96,300,000	100,500,000
Collateralized mortgage obligations (CMO)
Available-for-Sale Debt Securities
Amortized Cost	515,541,000	526,796,000
Gross Unrealized Gain	312,000	113,000
Gross Unrealized Loss	86,970,000	95,967,000
Allowance for Credit Losses	0	0
Fair Value	428,883,000	430,942,000
Fannie Mae (FNMA) mortgage-backed securities (MBS)
Available-for-Sale Debt Securities
Amortized Cost	3,265,466,000	3,305,418,000
Gross Unrealized Gain	918,000	172,000
Gross Unrealized Loss	476,980,000	550,011,000
Allowance for Credit Losses	0	0
Fair Value	2,789,404,000	2,755,579,000
Held-to-Maturity Debt Securities
Amortized Cost	822,843,000	831,325,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	103,107,000	116,600,000
Beginning balance	0	0
Fair Value	719,736,000	714,725,000
Freddie Mac (FHLMC) MBS
Available-for-Sale Debt Securities
Amortized Cost	116,803,000	118,605,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	10,793,000	13,091,000
Allowance for Credit Losses	0	0
Fair Value	106,010,000	105,514,000
Ginnie Mae (GNMA) MBS
Available-for-Sale Debt Securities
Amortized Cost	43,505,000	44,578,000
Gross Unrealized Gain	17,000	0
Gross Unrealized Loss	3,138,000	3,902,000
Allowance for Credit Losses	0	0
Fair Value	40,384,000	40,676,000
Government-sponsored enterprises (GSE) agency notes
Available-for-Sale Debt Securities
Amortized Cost	222,226,000	222,869,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	38,830,000	44,932,000
Allowance for Credit Losses	0	0
Fair Value	183,396,000	177,937,000
State and political subdivisions
Held-to-Maturity Debt Securities
Amortized Cost	183,573,000	183,843,000
Gross Unrealized Gain	57,000	247,000
Gross Unrealized Loss	4,621,000	3,297,000
Beginning balance	6,000	7,000	$ 8,000	$ 8,000
Fair Value	$ 179,003,000	$ 180,786,000