INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023	Mar. 31, 2023	Dec. 31, 2022
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,464,535	$ 1,447,637
Allowance for Credit Losses	(73)	(69)	$ (82)	$ (75)
Gross Unrealized Gains	39	112
Gross Unrealized Losses	(50,082)	(44,736)
Estimated Fair Value	1,414,419	1,402,944
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	712,985	732,636
Allowance for Credit Losses	0	0
Gross Unrealized Gains	8	34
Gross Unrealized Losses	(11,697)	(11,793)
Estimated Fair Value	701,296	720,877
U.S. government-sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,020	1,023
Allowance for Credit Losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(40)	(38)
Estimated Fair Value	980	985
State, county and municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	28,136	28,986
Allowance for Credit Losses	0	0
Gross Unrealized Gains	5	9
Gross Unrealized Losses	(1,137)	(944)
Estimated Fair Value	27,004	28,051
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	10,946	10,946
Allowance for Credit Losses	(73)	(69)
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(859)	(850)
Estimated Fair Value	10,014	10,027
SBA pool securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	80,164	53,033
Allowance for Credit Losses	0	0
Gross Unrealized Gains	2	2
Gross Unrealized Losses	(1,737)	(1,519)
Estimated Fair Value	78,429	51,516
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	631,284	621,013
Allowance for Credit Losses	0	0
Gross Unrealized Gains	24	67
Gross Unrealized Losses	(34,612)	(29,592)
Estimated Fair Value	$ 596,696	$ 591,488