INVESTMENTS - Estimated Fair Values of Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Fair Value
Total available-for-sale debt securities	$ 1,244,335	$ 1,465,896
Amortized Cost
Total available-for-sale debt securities	1,411,343	1,466,350
Fair Value
Total held-to-maturity debt securities	226,030	0
Amortized Cost
Total held-to-maturity debt securities	265,648	0
U.S. treasuries and government agencies
Fair Value
One year or less	0	12,029
One to five years	92,805	56,510
Five to ten years	0	0
After ten years	0	0
Total available-for-sale debt securities	92,805	68,539
Amortized Cost
One year or less	0	11,995
One to five years	100,740	56,492
Five to ten years	0	0
After ten years	0	0
Total available-for-sale debt securities	100,740	68,487
State and municipal
Fair Value
One year or less	4,297	12,821
One to five years	68,727	27,408
Five to ten years	31,787	42,960
After ten years	172,128	243,213
Total available-for-sale debt securities	276,939	326,402
Amortized Cost
One year or less	4,306	12,709
One to five years	71,754	26,637
Five to ten years	37,090	42,661
After ten years	229,342	241,279
Total available-for-sale debt securities	342,492	323,286
Mortgage-backed and asset-backed
Fair Value
One year or less	5,602	9,272
One to five years	48,806	14,752
Five to ten years	318,785	388,918
After ten years	501,398	658,013
Total available-for-sale debt securities	874,591	1,070,955
Amortized Cost
One year or less	5,639	9,239
One to five years	50,257	14,575
Five to ten years	353,118	390,569
After ten years	559,097	660,194
Total available-for-sale debt securities	968,111	1,074,577
Fair Value
One year or less	0	0
One to five years	0	0
Five to ten years	36,205	0
After ten years	189,825	0
Total held-to-maturity debt securities	226,030	0
Amortized Cost
One year or less	0	0
One to five years	0	0
Five to ten years	40,229	0
After ten years	225,419	0
Total held-to-maturity debt securities	$ 265,648	$ 0