INVESTMENTS - Amortized Cost and Estimated Fair Values of Investments (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Available-for-sale debt securities:
Total available-for-sale debt securities	$ 1,226,968	$ 1,220,819
Gross Unrealized Gains	83	182
Gross Unrealized Losses	(125,205)	(118,320)
Investments available-for-sale	1,101,846	1,102,681
Held-to-maturity debt securities:
Total held-to-maturity debt securities	226,233	236,165
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(38,844)	(35,754)
Total held-to-maturity debt securities	187,389	200,411
Total debt securities
Amortized Cost	1,453,201	1,456,984
Gross Unrealized Gains	83	182
Gross Unrealized Losses	(164,049)	(154,074)
Estimated Fair Value	1,289,235	1,303,092
U.S. treasuries and government agencies
Available-for-sale debt securities:
Total available-for-sale debt securities	87,052	101,678
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4,093)	(4,751)
Investments available-for-sale	82,959	96,927
State and municipal
Available-for-sale debt securities:
Total available-for-sale debt securities	310,073	311,505
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(48,179)	(43,292)
Investments available-for-sale	261,895	268,214
Mortgage-backed and asset-backed
Available-for-sale debt securities:
Total available-for-sale debt securities	829,843	807,636
Gross Unrealized Gains	82	181
Gross Unrealized Losses	(72,933)	(70,277)
Investments available-for-sale	756,992	737,540
Held-to-maturity debt securities:
Total held-to-maturity debt securities	226,233	236,165
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(38,844)	(35,754)
Total held-to-maturity debt securities	$ 187,389	$ 200,411