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INVESTMENT SECURITIES - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale and Held-to-Maturity Investment Securities (Details) - USD ($)	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Available-for-Sale Debt Securities
Amortized Cost	$ 4,758,199,000	$ 4,834,550,000
Gross Unrealized Gain	4,000	0
Gross Unrealized Loss	671,744,000	741,490,000
Allowance for Credit Losses	0	0
Fair Value	4,086,459,000	4,093,060,000
Held-to-Maturity Debt Securities
Amortized Cost	1,094,808,000	1,111,629,000
Gross Unrealized Gain	2,023,000	534,000
Gross Unrealized Loss	60,966,000	72,049,000
Allowance for Credit Losses	9,000	10,000
Fair Value	1,035,856,000	1,040,104,000
Available for sale securities transfers to held to maturity unrealized losses	(137,300,000)
Collateralized mortgage obligation (CMO)
Available-for-Sale Debt Securities
Amortized Cost	598,648,000	608,834,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	92,512,000	102,454,000
Allowance for Credit Losses	0	0
Fair Value	506,136,000	506,380,000
Fannie Mae (FNMA) mortgage-backed securities (MBS)
Available-for-Sale Debt Securities
Amortized Cost	3,755,800,000	3,823,036,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	519,977,000	572,778,000
Allowance for Credit Losses	0	0
Fair Value	3,235,823,000	3,250,258,000
Held-to-Maturity Debt Securities
Amortized Cost	902,774,000	909,498,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	60,122,000	68,677,000
Allowance for Credit Losses	0	0
Fair Value	842,652,000	840,821,000
Freddie Mac (FHLMC) MBS
Available-for-Sale Debt Securities
Amortized Cost	133,514,000	135,554,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	11,425,000	13,555,000
Allowance for Credit Losses	0	0
Fair Value	122,089,000	121,999,000
Ginnie Mae (GNMA) MBS
Available-for-Sale Debt Securities
Amortized Cost	42,869,000	39,116,000
Gross Unrealized Gain	4,000	0
Gross Unrealized Loss	2,631,000	2,978,000
Allowance for Credit Losses	0	0
Fair Value	40,242,000	36,138,000
Government-sponsored enterprises (GSE) agency notes
Available-for-Sale Debt Securities
Amortized Cost	227,368,000	228,010,000
Gross Unrealized Gain	0	0
Gross Unrealized Loss	45,199,000	49,725,000
Allowance for Credit Losses	0	0
Fair Value	182,169,000	178,285,000
State and political subdivisions
Held-to-Maturity Debt Securities
Amortized Cost	192,034,000	201,631,000
Gross Unrealized Gain	2,023,000	532,000
Gross Unrealized Loss	844,000	3,372,000
Allowance for Credit Losses	9,000	10,000	$ 4,000	$ 4,000
Fair Value	$ 193,204,000	198,781,000
Available for sale securities transfers to held to maturity unrealized losses		(142,800,000)
Foreign bonds
Held-to-Maturity Debt Securities
Amortized Cost		500,000
Gross Unrealized Gain		2,000
Gross Unrealized Loss		0
Allowance for Credit Losses		0
Fair Value		$ 502,000