INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Mar. 31, 2024	Dec. 31, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,578,537		$ 1,447,637
Allowance for Credit Losses	(68)	$ (73)	(69)	$ (82)	$ (82)	$ (75)
Gross Unrealized Gains	749		112
Gross Unrealized Losses	(48,171)		(44,736)
Estimated Fair Value	1,531,047		1,402,944
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	765,274		732,636
Allowance for Credit Losses	0		0
Gross Unrealized Gains	142		34
Gross Unrealized Losses	(10,204)		(11,793)
Estimated Fair Value	755,212		720,877
U.S. government-sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,016		1,023
Allowance for Credit Losses	0		0
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(35)		(38)
Estimated Fair Value	981		985
State, county and municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	27,848		28,986
Allowance for Credit Losses	0		0
Gross Unrealized Gains	0		9
Gross Unrealized Losses	(1,288)		(944)
Estimated Fair Value	26,560		28,051
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,946		10,946
Allowance for Credit Losses	(68)		(69)
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(877)		(850)
Estimated Fair Value	10,001		10,027
SBA pool securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	77,850		53,033
Allowance for Credit Losses	0		0
Gross Unrealized Gains	2		2
Gross Unrealized Losses	(1,587)		(1,519)
Estimated Fair Value	76,265		51,516
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	695,603		621,013
Allowance for Credit Losses	0		0
Gross Unrealized Gains	605		67
Gross Unrealized Losses	(34,180)		(29,592)
Estimated Fair Value	$ 662,028		$ 591,488