INVESTMENTS - Amortized Cost and Estimated Fair Values of Investments (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Available-for-sale debt securities:
Amortized Cost	$ 1,366,843	$ 1,466,350
Gross Unrealized Gains	77	14,966
Gross Unrealized Losses	(152,382)	(15,420)
Investments available-for-sale (at fair value)	1,214,538	1,465,896
Held-to-maturity debt securities
Amortized Cost	259,452	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(39,329)	0
Investments held-to-maturity (at fair value)	220,123	0
Total debt securities
Book value of debt securities pledged as collateral	1,626,295	1,466,350
Gross Unrealized Gains	77	14,966
Gross Unrealized Losses	(191,711)	(15,420)
Estimated Fair Value	1,434,661	1,465,896
U.S. treasuries and government agencies
Available-for-sale debt securities:
Amortized Cost	100,926	68,487
Gross Unrealized Gains	0	202
Gross Unrealized Losses	(7,304)	(150)
Investments available-for-sale (at fair value)	93,622	68,539
State and municipal
Available-for-sale debt securities:
Amortized Cost	322,519	323,286
Gross Unrealized Gains	4	6,561
Gross Unrealized Losses	(56,526)	(3,445)
Investments available-for-sale (at fair value)	265,997	326,402
Mortgage-backed and asset-backed
Available-for-sale debt securities:
Amortized Cost	943,398	1,074,577
Gross Unrealized Gains	73	8,203
Gross Unrealized Losses	(88,552)	(11,825)
Investments available-for-sale (at fair value)	854,919	1,070,955
Held-to-maturity debt securities
Amortized Cost	259,452	0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(39,329)	0
Investments held-to-maturity (at fair value)	$ 220,123	$ 0