INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,459,318		$ 1,447,637
Allowance for Credit Losses	(66)	$ (68)	(69)	$ (80)	$ (82)	$ (75)
Gross Unrealized Gains	6,729		112
Gross Unrealized Losses	(24,429)		(44,736)
Estimated Fair Value	1,441,552		1,402,944
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	631,992		732,636
Allowance for Credit Losses	0		0
Gross Unrealized Gains	2,746		34
Gross Unrealized Losses	(4,067)		(11,793)
Estimated Fair Value	630,671		720,877
U.S. government-sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,013		1,023
Allowance for Credit Losses	0		0
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(18)		(38)
Estimated Fair Value	995		985
State, county and municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	26,652		28,986
Allowance for Credit Losses	0		0
Gross Unrealized Gains	23		9
Gross Unrealized Losses	(746)		(944)
Estimated Fair Value	25,929		28,051
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,946		10,946
Allowance for Credit Losses	(66)		(69)
Gross Unrealized Gains	10		0
Gross Unrealized Losses	(664)		(850)
Estimated Fair Value	10,226		10,027
SBA pool securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	75,276		53,033
Allowance for Credit Losses	0		0
Gross Unrealized Gains	2		2
Gross Unrealized Losses	(1,086)		(1,519)
Estimated Fair Value	74,192		51,516
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	713,439		621,013
Allowance for Credit Losses	0		0
Gross Unrealized Gains	3,948		67
Gross Unrealized Losses	(17,848)		(29,592)
Estimated Fair Value	$ 699,539		$ 591,488