INVESTMENTS - Amortized Cost and Estimated Fair Values of Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Available-for-sale debt securities:
Total available-for-sale debt securities	$ 1,327,249	$ 1,366,843
Gross Unrealized Gains	70	77
Gross Unrealized Losses	(131,591)	(152,382)
Investments available-for-sale	1,195,728	1,214,538
Held-to-maturity debt securities:
Total held-to-maturity debt securities	254,219	259,452
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(34,802)	(39,329)
Total held-to-maturity debt securities	219,417	220,123
Total debt securities
Amortized Cost	1,581,468	1,626,295
Gross Unrealized Gains	70	77
Gross Unrealized Losses	(166,393)	(191,711)
Estimated Fair Value	1,415,145	1,434,661
U.S. treasuries and government agencies
Available-for-sale debt securities:
Total available-for-sale debt securities	101,112	100,926
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(6,022)	(7,304)
Investments available-for-sale	95,090	93,622
State and municipal
Available-for-sale debt securities:
Total available-for-sale debt securities	320,799	322,519
Gross Unrealized Gains	5	4
Gross Unrealized Losses	(47,876)	(56,526)
Investments available-for-sale	272,928	265,997
Mortgage-backed and asset-backed
Available-for-sale debt securities:
Total available-for-sale debt securities	905,338	943,398
Gross Unrealized Gains	65	73
Gross Unrealized Losses	(77,693)	(88,552)
Investments available-for-sale	827,710	854,919
Held-to-maturity debt securities:
Total held-to-maturity debt securities	254,219	259,452
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(34,802)	(39,329)
Total held-to-maturity debt securities	$ 219,417	$ 220,123