INVESTMENT SECURITIES - Schedule of Amortized Cost and Estimated Fair Value of Available-for-Sale and Held-to-Maturity Investment Securities (Details) - USD ($)	Jun. 30, 2025	Mar. 31, 2025	Dec. 31, 2024	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023
Available-for-Sale Debt Securities
Amortized Cost	$ 4,080,394,000		$ 4,218,266,000
Gross Unrealized Gain	1,639,000		285,000
Gross Unrealized Loss	587,250,000		707,903,000
Allowance for Credit Losses	0		0
Fair Value	3,494,783,000		3,510,648,000
Held-to-Maturity Debt Securities
Amortized Cost	994,346,000		1,015,168,000
Gross Unrealized Gain	113,000		247,000
Gross Unrealized Loss	110,193,000		119,897,000
Beginning balance	6,000	$ 6,000	7,000	$ 7,000	$ 8,000	$ 8,000
Fair Value	884,260,000		895,511,000
Available for sale securities transfers to held to maturity unrealized losses	92,000,000.0		100,500,000
Collateralized mortgage obligations (CMO)
Available-for-Sale Debt Securities
Amortized Cost	503,898,000		526,796,000
Gross Unrealized Gain	365,000		113,000
Gross Unrealized Loss	82,534,000		95,967,000
Allowance for Credit Losses	0		0
Fair Value	421,729,000		430,942,000
Fannie Mae (FNMA) mortgage-backed securities (MBS)
Available-for-Sale Debt Securities
Amortized Cost	3,197,683,000		3,305,418,000
Gross Unrealized Gain	1,257,000		172,000
Gross Unrealized Loss	454,725,000		550,011,000
Allowance for Credit Losses	0		0
Fair Value	2,744,215,000		2,755,579,000
Held-to-Maturity Debt Securities
Amortized Cost	811,583,000		831,325,000
Gross Unrealized Gain	0		0
Gross Unrealized Loss	105,626,000		116,600,000
Beginning balance	0		0
Fair Value	705,957,000		714,725,000
Freddie Mac (FHLMC) MBS
Available-for-Sale Debt Securities
Amortized Cost	114,918,000		118,605,000
Gross Unrealized Gain	0		0
Gross Unrealized Loss	9,762,000		13,091,000
Allowance for Credit Losses	0		0
Fair Value	105,156,000		105,514,000
Ginnie Mae (GNMA) MBS
Available-for-Sale Debt Securities
Amortized Cost	42,312,000		44,578,000
Gross Unrealized Gain	17,000		0
Gross Unrealized Loss	2,954,000		3,902,000
Allowance for Credit Losses	0		0
Fair Value	39,375,000		40,676,000
Government-sponsored enterprises (GSE) agency notes
Available-for-Sale Debt Securities
Amortized Cost	221,583,000		222,869,000
Gross Unrealized Gain	0		0
Gross Unrealized Loss	37,275,000		44,932,000
Allowance for Credit Losses	0		0
Fair Value	184,308,000		177,937,000
State and political subdivisions
Held-to-Maturity Debt Securities
Amortized Cost	182,763,000		183,843,000
Gross Unrealized Gain	113,000		247,000
Gross Unrealized Loss	4,567,000		3,297,000
Beginning balance	6,000	$ 6,000	7,000	$ 7,000	$ 8,000	$ 8,000
Fair Value	$ 178,303,000		$ 180,786,000