INVESTMENTS - Estimated Fair Values of Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Fair Value
Total available-for-sale debt securities	$ 1,214,538	$ 1,465,896
Amortized Cost
Amortized Cost	1,366,843	1,466,350
Fair Value
Total held-to-maturity debt securities	220,123	0
Amortized Cost
Amortized Cost	259,452	0
U.S. treasuries and government agencies
Fair Value
One year or less	0	12,029
One to five years	93,622	56,510
Five to ten years	0	0
After ten years	0	0
Total available-for-sale debt securities	93,622	68,539
Amortized Cost
One year or less	0	11,995
One to five years	100,926	56,492
Five to ten years	0	0
After ten years	0	0
Amortized Cost	100,926	68,487
State and municipal
Fair Value
One year or less	8,694	12,821
One to five years	51,576	27,408
Five to ten years	28,806	42,960
After ten years	176,921	243,213
Total available-for-sale debt securities	265,997	326,402
Amortized Cost
One year or less	8,783	12,709
One to five years	53,948	26,637
Five to ten years	34,042	42,661
After ten years	225,746	241,279
Amortized Cost	322,519	323,286
Mortgage-backed and asset-backed
Fair Value
One year or less	7,622	9,272
One to five years	45,366	14,752
Five to ten years	303,697	388,918
After ten years	498,234	658,013
Total available-for-sale debt securities	854,919	1,070,955
Amortized Cost
One year or less	7,704	9,239
One to five years	46,802	14,575
Five to ten years	335,285	390,569
After ten years	553,607	660,194
Amortized Cost	943,398	1,074,577
Fair Value
One year or less	0	0
One to five years	0	0
Five to ten years	35,304	0
After ten years	184,819	0
Total held-to-maturity debt securities	220,123	0
Amortized Cost
One year or less	0	0
One to five years	0	0
Five to ten years	39,213	0
After ten years	220,239	0
Amortized Cost	259,452	0
Corporate debt
Fair Value
After ten years	0	0
Amortized Cost
After ten years	$ 0	$ 0