INVESTMENT SECURITIES - Schedule of Maturities of Investment Securities Available-for-Sale and Held-to-Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Available for Sale, Amortized Cost
Within one year	$ 0	$ 0
After one year but within five years	87,314	83,014
After five years but within ten years	577,578	465,777
After ten years	3,919,298	4,285,759
Amortized Cost	4,584,190	4,834,550
Available for Sale, Fair Value
Within one year	0	0
After one year but within five years	81,548	77,499
After five years but within ten years	465,454	398,607
After ten years	3,144,539	3,616,954
Available-for-sale, fair value total	3,691,541	4,093,060
Held to Maturity, Amortized Cost
Within one year	0	731
After one year but within five years	9,793	9,530
After five years but within ten years	45,306	46,170
After ten years	1,013,780	1,055,198
Investment securities held-to-maturity, net	1,068,879	1,111,629
Held to Maturity, Fair Value
Within one year	0	732
After one year but within five years	9,373	9,476
After five years but within ten years	42,615	45,944
After ten years	875,692	983,952
Held-to-maturity, fair value total	$ 927,680	$ 1,040,104