INVESTMENT SECURITIES - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale and Held-to-Maturity Investment Securities (Details) - USD ($)	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Available-for-Sale Debt Securities
Amortized Cost	$ 4,444,676,000	$ 4,504,342,000
Gross Unrealized Gain	119,000	168,000
Gross Unrealized Loss	710,566,000	657,973,000
Allowance for Credit Losses	0	0
Fair Value	3,734,229,000	3,846,537,000
Held-to-Maturity Debt Securities
Amortized Cost	1,049,815,000	1,058,565,000
Gross Unrealized Gain	1,368,000	2,665,000
Gross Unrealized Loss	101,448,000	75,291,000
Allowance for Credit Losses	8,000	8,000
Fair Value	949,727,000	985,931,000
Available for sale securities transfers to held to maturity unrealized losses	115,600,000
Collateralized mortgage obligation (CMO)
Available-for-Sale Debt Securities
Amortized Cost	551,883,000	560,952,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	99,992,000	96,333,000
Allowance for Credit Losses	0	0
Fair Value	451,891,000	464,619,000
Fannie Mae (FNMA) mortgage-backed securities (MBS)
Available-for-Sale Debt Securities
Amortized Cost	3,495,526,000	3,544,762,000
Gross Unrealized Gain	118,000	162,000
Gross Unrealized Loss	548,295,000	502,574,000
Allowance for Credit Losses	0	0
Fair Value	2,947,349,000	3,042,350,000
Held-to-Maturity Debt Securities
Amortized Cost	864,584,000	872,653,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	99,912,000	74,332,000
Allowance for Credit Losses	0	0
Fair Value	764,672,000	798,321,000
Freddie Mac (FHLMC) MBS
Available-for-Sale Debt Securities
Amortized Cost	124,992,000	126,856,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	13,241,000	11,324,000
Allowance for Credit Losses	0	0
Fair Value	111,751,000	115,532,000
Ginnie Mae (GNMA) MBS
Available-for-Sale Debt Securities
Amortized Cost	47,478,000	46,333,000
Gross Unrealized Gain	1,000	6,000
Gross Unrealized Loss	3,539,000	2,999,000
Allowance for Credit Losses	0	0
Fair Value	43,940,000	43,340,000
Government-sponsored enterprises (GSE) agency notes
Available-for-Sale Debt Securities
Amortized Cost	224,797,000	225,439,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	45,499,000	44,743,000
Allowance for Credit Losses	0	0
Fair Value	179,298,000	180,696,000
State and political subdivisions
Held-to-Maturity Debt Securities
Amortized Cost	185,231,000	185,912,000
Gross Unrealized Gain	1,368,000	2,665,000
Gross Unrealized Loss	1,536,000	959,000
Allowance for Credit Losses	8,000	8,000	$ 9,000	$ 10,000
Fair Value	$ 185,055,000	187,610,000
Available for sale securities transfers to held to maturity unrealized losses		$ 120,400,000

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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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).

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Amount of accumulated unrecognized gain on investment in debt security measured at amortized cost (held-to-maturity).

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Debt Securities, Available-For-Sale, Transfers To Held To Maturity Unrealized Gains (Losses)

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