INVESTMENT SECURITIES - Schedule of Gross Unrealized Losses and Fair Value of Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Estimated Fair Value
Less than 12 months, estimated fair value	$ 260,536	$ 1,405,288
12 months or more, estimated fair value	1,159,183	27,331
Total estimated fair value	1,419,719	1,432,619
Unrealized Losses
Less than 12 months, unrealized losses	(3,934)	(56,816)
12 months or more, unrealized losses	(74,135)	(2,318)
Total unrealized losses	(78,069)	(59,134)
U.S. Treasuries
Estimated Fair Value
Less than 12 months, estimated fair value	230,519	725,250
12 months or more, estimated fair value	530,077	0
Total estimated fair value	760,596	725,250
Unrealized Losses
Less than 12 months, unrealized losses	(2,956)	(16,381)
12 months or more, unrealized losses	(17,602)	0
Total unrealized losses	(20,558)	(16,381)
U.S. government-sponsored agencies
Estimated Fair Value
Less than 12 months, estimated fair value	0	979
12 months or more, estimated fair value	969	0
Total estimated fair value	969	979
Unrealized Losses
Less than 12 months, unrealized losses	0	(57)
12 months or more, unrealized losses	(57)	0
Total unrealized losses	(57)	(57)
State, county and municipal securities
Estimated Fair Value
Less than 12 months, estimated fair value	6,739	27,438
12 months or more, estimated fair value	19,549	0
Total estimated fair value	26,288	27,438
Unrealized Losses
Less than 12 months, unrealized losses	(135)	(1,180)
12 months or more, unrealized losses	(1,654)	0
Total unrealized losses	(1,789)	(1,180)
Corporate debt securities
Estimated Fair Value
Less than 12 months, estimated fair value	491	13,271
12 months or more, estimated fair value	13,045	1,155
Total estimated fair value	13,536	14,426
Unrealized Losses
Less than 12 months, unrealized losses	(9)	(126)
12 months or more, unrealized losses	(1,046)	(270)
Total unrealized losses	(1,055)	(396)
SBA pool securities
Estimated Fair Value
Less than 12 months, estimated fair value	43	17,806
12 months or more, estimated fair value	21,547	9,329
Total estimated fair value	21,590	27,135
Unrealized Losses
Less than 12 months, unrealized losses	0	(1,298)
12 months or more, unrealized losses	(2,085)	(729)
Total unrealized losses	(2,085)	(2,027)
Mortgage-backed securities
Estimated Fair Value
Less than 12 months, estimated fair value	22,744	620,544
12 months or more, estimated fair value	573,996	16,847
Total estimated fair value	596,740	637,391
Unrealized Losses
Less than 12 months, unrealized losses	(834)	(37,774)
12 months or more, unrealized losses	(51,691)	(1,319)
Total unrealized losses	$ (52,525)	$ (39,093)