INVESTMENT SECURITIES - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale and Held-to-Maturity Investment Securities (Details) - USD ($)	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Available-for-Sale Debt Securities
Amortized Cost	$ 4,374,333,000		$ 4,504,342,000
Gross Unrealized Gain	330,000		168,000
Gross Unrealized Loss	722,750,000		657,973,000
Allowance for Credit Losses	0		0
Fair Value	3,651,913,000		3,846,537,000
Held-to-Maturity Debt Securities
Amortized Cost	1,038,861,000		1,058,565,000
Gross Unrealized Gain	527,000		2,665,000
Gross Unrealized Loss	109,713,000		75,291,000
Allowance for Credit Losses	7,000		8,000
Fair Value	929,668,000		985,931,000
Available for sale securities transfers to held to maturity unrealized losses	110,600,000
Collateralized mortgage obligation (CMO)
Available-for-Sale Debt Securities
Amortized Cost	550,076,000		560,952,000
Gross Unrealized Gain	193,000		0
Gross Unrealized Loss	100,871,000		96,333,000
Allowance for Credit Losses	0		0
Fair Value	449,398,000		464,619,000
Fannie Mae (FNMA) mortgage-backed securities (MBS)
Available-for-Sale Debt Securities
Amortized Cost	3,430,171,000		3,544,762,000
Gross Unrealized Gain	136,000		162,000
Gross Unrealized Loss	558,186,000		502,574,000
Allowance for Credit Losses	0		0
Fair Value	2,872,121,000		3,042,350,000
Held-to-Maturity Debt Securities
Amortized Cost	853,910,000		872,653,000
Gross Unrealized Gain	0		0
Gross Unrealized Loss	106,377,000		74,332,000
Allowance for Credit Losses	0		0
Fair Value	747,533,000		798,321,000
Freddie Mac (FHLMC) MBS
Available-for-Sale Debt Securities
Amortized Cost	122,622,000		126,856,000
Gross Unrealized Gain	0		0
Gross Unrealized Loss	13,410,000		11,324,000
Allowance for Credit Losses	0		0
Fair Value	109,212,000		115,532,000
Ginnie Mae (GNMA) MBS
Available-for-Sale Debt Securities
Amortized Cost	47,310,000		46,333,000
Gross Unrealized Gain	1,000		6,000
Gross Unrealized Loss	4,062,000		2,999,000
Allowance for Credit Losses	0		0
Fair Value	43,249,000		43,340,000
Government-sponsored enterprises (GSE) agency notes
Available-for-Sale Debt Securities
Amortized Cost	224,154,000		225,439,000
Gross Unrealized Gain	0		0
Gross Unrealized Loss	46,221,000		44,743,000
Allowance for Credit Losses	0		0
Fair Value	177,933,000		180,696,000
State and political subdivisions
Held-to-Maturity Debt Securities
Amortized Cost	184,951,000		185,912,000
Gross Unrealized Gain	527,000		2,665,000
Gross Unrealized Loss	3,336,000		959,000
Allowance for Credit Losses	7,000	$ 8,000	8,000	$ 8,000	$ 9,000	$ 10,000
Fair Value	$ 182,135,000		187,610,000
Available for sale securities transfers to held to maturity unrealized losses			$ 120,400,000