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, 2022	Dec. 31, 2021
Amortized Cost
Due in one year or less	$ 4,646	$ 6,954
Due after one through five years	14,329	5,097
Due after five through ten years	176,931	120,460
Due after ten years	1,553,003	1,464,460
Total debt securities with a single maturity date	1,748,909	1,596,971
Total investment securities	2,376,492	2,268,655
Fair Value
Due in one year or less	4,617	6,965
Due after one through five years	13,776	5,309
Due after five through ten years	161,885	126,816
Due after ten years	1,284,905	1,537,856
Total debt securities with a single maturity date	1,465,183	1,676,946
Total investment securities	1,983,972	2,344,551
Amortized Cost
Due in one year or less	6,428	6,971
Due after one through five years	71,303	30,272
Due after five through ten years	156,564	177,203
Due after ten years	1,280,606	1,215,812
Total debt securities with a single maturity date	1,514,901	1,430,258
Amortized Cost	2,311,041	2,180,047
Fair Value
Due in one year or less	6,439	6,995
Due after one through five years	67,777	31,946
Due after five through ten years	139,284	180,129
Due after ten years	978,157	1,231,568
Total debt securities with a single maturity date	1,191,657	1,450,638
Investment securities held to maturity	1,867,088	2,202,503
U.S. Government-sponsored mortgage-backed securities
Amortized Cost
U.S. Government-sponsored mortgage-backed securities	627,583	671,684
Fair Value
U.S. Government-sponsored mortgage-backed securities	518,789	667,605
Total investment securities	518,789	667,605
Amortized Cost
U.S. Government-sponsored mortgage-backed securities	796,140	749,789
Amortized Cost	796,140	749,789
Fair Value
U.S. Government-sponsored mortgage-backed securities	675,431	751,865
Investment securities held to maturity	$ 675,431	$ 751,865