INVESTMENT SECURITIES - Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized Cost
Due in one year or less	$ 3,403	$ 2,822
Due after one through five years	27,736	11,694
Due after five through ten years	127,442	169,729
Due after ten years	1,187,823	1,480,472
Total debt securities with a single maturity date	1,346,404	1,664,717
Total investment securities	1,882,934	2,273,347
Fair Value
Due in one year or less	3,356	2,809
Due after one through five years	25,266	11,265
Due after five through ten years	110,668	161,211
Due after ten years	940,883	1,293,103
Total debt securities with a single maturity date	1,080,173	1,468,388
Total investment securities	1,500,136	1,976,661
Amortized Cost
Due in one year or less	9,422	13,697
Due after one through five years	116,894	80,697
Due after five through ten years	134,603	147,078
Due after ten years	1,226,612	1,269,826
Total debt securities with a single maturity date	1,487,531	1,511,298
Total investment securities	2,213,833	2,287,372
Fair Value
Due in one year or less	9,397	13,749
Due after one through five years	106,277	76,453
Due after five through ten years	117,134	135,027
Due after ten years	917,278	1,020,477
Total debt securities with a single maturity date	1,150,086	1,245,706
Total investment securities	1,741,225	1,907,865
U.S. Government-sponsored mortgage-backed securities
Amortized Cost
U.S. Government-sponsored mortgage-backed securities	536,530	608,630
Fair Value
U.S. Government-sponsored mortgage-backed securities	419,963	508,273
Total investment securities	419,963	508,273
Amortized Cost
U.S. Government-sponsored mortgage-backed securities	726,302	776,074
Total investment securities	726,302	776,074
Fair Value
U.S. Government-sponsored mortgage-backed securities	591,139	662,159
Total investment securities	$ 591,139	$ 662,159