INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Investment Securities Available for Sale (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 1,524,818		$ 1,559,005
Allowance for Credit Losses	(82)	$ (82)	(75)	$ (88)	$ 0	$ 0
Gross Unrealized Gains	20		264
Gross Unrealized Losses	(64,400)		(59,134)
Estimated Fair Value	1,460,356		1,500,060
U.S. Treasuries
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	779,382		775,784
Allowance for Credit Losses	0		0
Gross Unrealized Gains	0		131
Gross Unrealized Losses	(20,716)		(16,381)
Estimated Fair Value	758,666		759,534
U.S. government-sponsored agencies
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	1,029		1,036
Allowance for Credit Losses	0		0
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(57)		(57)
Estimated Fair Value	972		979
State, county and municipal securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	33,340		35,358
Allowance for Credit Losses	0		0
Gross Unrealized Gains	1		17
Gross Unrealized Losses	(1,113)		(1,180)
Estimated Fair Value	32,228		34,195
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	15,897		16,397
Allowance for Credit Losses	(82)		(75)
Gross Unrealized Gains	0		0
Gross Unrealized Losses	(760)		(396)
Estimated Fair Value	15,055		15,926
SBA pool securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	25,799		29,422
Allowance for Credit Losses	0		0
Gross Unrealized Gains	3		3
Gross Unrealized Losses	(1,976)		(2,027)
Estimated Fair Value	23,826		27,398
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	669,371		701,008
Allowance for Credit Losses	0		0
Gross Unrealized Gains	16		113
Gross Unrealized Losses	(39,778)		(39,093)
Estimated Fair Value	$ 629,609		$ 662,028