INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,541,142	$ 1,559,005
Allowance for Credit Losses	(82)	(75)	$ 0	$ 0
Gross Unrealized Gains	1,252	264
Gross Unrealized Losses	(45,476)	(59,134)
Estimated Fair Value	1,496,836	1,500,060
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	776,583	775,784
Allowance for Credit Losses	0	0
Gross Unrealized Gains	911	131
Gross Unrealized Losses	(11,365)	(16,381)
Estimated Fair Value	766,129	759,534
U.S. government-sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,032	1,036
Allowance for Credit Losses	0	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(45)	(57)
Estimated Fair Value	987	979
State, county and municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	33,965	35,358
Allowance for Credit Losses	0	0
Gross Unrealized Gains	21	17
Gross Unrealized Losses	(773)	(1,180)
Estimated Fair Value	33,213	34,195
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	16,397	16,397
Allowance for Credit Losses	(82)	(75)
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(705)	(396)
Estimated Fair Value	15,610	15,926
SBA pool securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	26,942	29,422
Allowance for Credit Losses	0	0
Gross Unrealized Gains	3	3
Gross Unrealized Losses	(1,603)	(2,027)
Estimated Fair Value	25,342	27,398
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	686,223	701,008
Allowance for Credit Losses	0	0
Gross Unrealized Gains	317	113
Gross Unrealized Losses	(30,985)	(39,093)
Estimated Fair Value	$ 655,555	$ 662,028