INVESTMENTS - Amortized Cost and Estimated Fair Values of Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Available-for-sale debt securities:
Total available-for-sale debt securities	$ 1,226,582	$ 1,220,819
Gross Unrealized Gains	83	182
Gross Unrealized Losses	(125,924)	(118,320)
Investments available-for-sale	1,100,741	1,102,681
Held-to-maturity debt securities:
Total held-to-maturity debt securities	231,354	236,165
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(38,556)	(35,754)
Total held-to-maturity debt securities	192,798	200,411
Total debt securities
Amortized Cost	1,457,936	1,456,984
Gross Unrealized Gains	83	182
Gross Unrealized Losses	(164,480)	(154,074)
Estimated Fair Value	1,293,539	1,303,092
U.S. treasuries and government agencies
Available-for-sale debt securities:
Total available-for-sale debt securities	96,866	101,678
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(4,630)	(4,751)
Investments available-for-sale	92,236	96,927
State and municipal
Available-for-sale debt securities:
Total available-for-sale debt securities	310,502	311,505
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(46,516)	(43,292)
Investments available-for-sale	263,986	268,214
Mortgage-backed and asset-backed
Available-for-sale debt securities:
Total available-for-sale debt securities	819,214	807,636
Gross Unrealized Gains	83	181
Gross Unrealized Losses	(74,778)	(70,277)
Investments available-for-sale	744,519	737,540
Held-to-maturity debt securities:
Total held-to-maturity debt securities	231,354	236,165
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(38,556)	(35,754)
Total held-to-maturity debt securities	$ 192,798	$ 200,411