INVESTMENTS - Summary of Investment Securities by Estimated Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Held-to-Maturity Amortized Cost
Amortized Cost	$ 81,236	$ 84,021
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	69,845	76,485
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	3,526,096	3,827,418
Available-for-Sale Market Value
Investment securities available-for-sale	3,044,361	3,409,648
One Year or Less [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	0
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	0
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	9,534
Available-for-Sale Market Value
Investment securities available-for-sale	9,435
After One Year Through Five Years [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	4,164
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	4,064
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	129,631
Available-for-Sale Market Value
Investment securities available-for-sale	117,854
After Five Years Through Ten Years [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	33,505
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	29,652
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	269,634
Available-for-Sale Market Value
Investment securities available-for-sale	228,912
After Ten Years [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	1,758
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	1,460
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	661,278
Available-for-Sale Market Value
Investment securities available-for-sale	529,076
Residential Mortgage Backed Securities [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	0	0
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	0	0
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	705,681	747,478
Available-for-Sale Market Value
Investment securities available-for-sale	584,483	650,063
Commercial Mortgage Backed Securities [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	33,399	35,363
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	27,441	31,249
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	599,969	676,934
Available-for-Sale Market Value
Investment securities available-for-sale	549,570	629,562
Collateralized Mortgage Backed Securities [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	8,410	9,280
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	7,228	8,453
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	488,590	538,970
Available-for-Sale Market Value
Investment securities available-for-sale	412,931	477,712
Asset-backed Securities [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	0	0
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	0	0
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	661,779	772,261
Available-for-Sale Market Value
Investment securities available-for-sale	$ 612,100	$ 711,325