INVESTMENTS - Amortized Cost and Estimated Fair Values of Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Available-for-sale debt securities:
Total available-for-sale debt securities	$ 1,239,762	$ 1,220,819
Gross Unrealized Gains	1,639	182
Gross Unrealized Losses	(92,345)	(118,320)
Investments available-for-sale	1,149,056	1,102,681
Held-to-maturity debt securities:
Total held-to-maturity debt securities	220,296	236,165
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(30,443)	(35,754)
Total held-to-maturity debt securities	189,853	200,411
Total debt securities
Amortized Cost	1,460,058	1,456,984
Gross Unrealized Gains	1,639	182
Gross Unrealized Losses	(122,788)	(154,074)
Estimated Fair Value	1,338,909	1,303,092
U.S. treasuries and government agencies
Available-for-sale debt securities:
Total available-for-sale debt securities	87,237	101,678
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2,430)	(4,751)
Investments available-for-sale	84,807	96,927
State and municipal
Available-for-sale debt securities:
Total available-for-sale debt securities	303,844	311,505
Gross Unrealized Gains	1	1
Gross Unrealized Losses	(38,656)	(43,292)
Investments available-for-sale	265,189	268,214
Mortgage-backed and asset-backed
Available-for-sale debt securities:
Total available-for-sale debt securities	848,681	807,636
Gross Unrealized Gains	1,638	181
Gross Unrealized Losses	(51,259)	(70,277)
Investments available-for-sale	799,060	737,540
Held-to-maturity debt securities:
Total held-to-maturity debt securities	220,296	236,165
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(30,443)	(35,754)
Total held-to-maturity debt securities	$ 189,853	$ 200,411