INVESTMENT SECURITIES - Amortized Cost and Fair Value of Available for Sale Securities and Held to Maturity Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Amortized Cost
Due in one year or less	$ 1,861	$ 2,822
Due after one through five years	21,853	11,694
Due after five through ten years	118,743	169,729
Due after ten years	1,312,894	1,480,472
Total debt securities with a single maturity date	1,455,351	1,664,717
Total investment securities	2,039,927	2,273,347
Fair Value
Due in one year or less	1,854	2,809
Due after one through five years	20,346	11,265
Due after five through ten years	113,564	161,211
Due after ten years	1,164,839	1,293,103
Total debt securities with a single maturity date	1,300,603	1,468,388
Total investment securities	1,794,208	1,976,661
Amortized Cost
Due in one year or less	12,168	13,697
Due after one through five years	112,941	80,697
Due after five through ten years	120,969	147,078
Due after ten years	1,258,569	1,269,826
Total debt securities with a single maturity date	1,504,647	1,511,298
Amortized Cost	2,263,426	2,287,372
Fair Value
Due in one year or less	12,225	13,749
Due after one through five years	105,185	76,453
Due after five through ten years	114,725	135,027
Due after ten years	1,045,755	1,020,477
Total debt securities with a single maturity date	1,277,890	1,245,706
Investment securities held to maturity	1,934,601	1,907,865
U.S. Government-sponsored mortgage-backed securities
Amortized Cost
U.S. Government-sponsored mortgage-backed securities	584,576	608,630
Fair Value
U.S. Government-sponsored mortgage-backed securities	493,605	508,273
Total investment securities	493,605	508,273
Amortized Cost
U.S. Government-sponsored mortgage-backed securities	758,779	776,074
Amortized Cost	758,779	776,074
Fair Value
U.S. Government-sponsored mortgage-backed securities	656,711	662,159
Investment securities held to maturity	$ 656,711	$ 662,159