INVESTMENTS - Estimated Fair Values of Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Fair Value
Total available-for-sale debt securities	$ 1,100,741	$ 1,102,681
Amortized Cost
Total available-for-sale debt securities	1,226,582	1,220,819
Fair Value
Total held-to-maturity debt securities	192,798	200,411
Amortized Cost
Total held-to-maturity debt securities	231,354	236,165
U.S. treasuries and government agencies
Fair Value
One year or less	12,922	17,798
One to five years	79,314	79,129
Five to ten years	0	0
After ten years	0	0
Total available-for-sale debt securities	92,236	96,927
Amortized Cost
One year or less	12,988	17,979
One to five years	83,878	83,699
Five to ten years	0	0
After ten years	0	0
Total available-for-sale debt securities	96,866	101,678
State and municipal
Fair Value
One year or less	28,318	22,345
One to five years	28,586	33,282
Five to ten years	48,992	46,355
After ten years	158,090	166,232
Total available-for-sale debt securities	263,986	268,214
Amortized Cost
One year or less	28,739	22,793
One to five years	29,770	34,288
Five to ten years	57,965	54,487
After ten years	194,028	199,937
Total available-for-sale debt securities	310,502	311,505
Mortgage-backed and asset-backed
Fair Value
One year or less	26,396	20,814
One to five years	27,290	29,823
Five to ten years	267,178	256,924
After ten years	423,655	429,979
Total available-for-sale debt securities	744,519	737,540
Amortized Cost
One year or less	26,704	21,111
One to five years	28,067	30,666
Five to ten years	292,078	280,209
After ten years	472,365	475,650
Total available-for-sale debt securities	819,214	807,636
Fair Value
One year or less	0	0
One to five years	0	0
Five to ten years	30,070	31,434
After ten years	162,728	168,977
Total held-to-maturity debt securities	192,798	200,411
Amortized Cost
One year or less	0	0
One to five years	0	0
Five to ten years	33,326	34,458
After ten years	198,028	201,707
Total held-to-maturity debt securities	$ 231,354	$ 236,165