INVESTMENT SECURITIES - Amortized Cost and Fair Value of Available for Sale Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Amortized Cost
Due in one year or less	$ 380,435
Due from one year to five years	439,956
Due from five to ten years	10,753
Due after ten years	20,533
Mortgage-backed securities	650,535
Amortized Cost	1,502,212	$ 1,559,005
Estimated Fair Value
Due in one year or less	375,844
Due from one year to five years	422,385
Due from five to ten years	9,897
Due after ten years	17,929
Mortgage-backed securities	598,026
Estimated Fair Value	1,424,081	1,500,060
Amortized Cost
Due in one year or less	0
Due from one year to five years	0
Due from five to ten years	0
Due after ten years	31,905
Mortgage-backed securities	109,954
Amortized Cost	141,859	134,864
Estimated Fair Value
Due in one year or less	0
Due from one year to five years	0
Due from five to ten years	0
Due after ten years	24,555
Mortgage-backed securities	91,134
Estimated Fair Value	$ 115,689	$ 114,538