INVESTMENTS - Summary of Investment Securities by Estimated Maturity (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Held-to-Maturity Amortized Cost
Amortized Cost	$ 88,057	$ 98,420
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	83,990	99,898
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	4,128,546	4,180,589
Available-for-Sale Market Value
Investment securities available-for-sale	3,843,580	4,207,846
One Year or Less [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	0
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	0
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	6,850
Available-for-Sale Market Value
Investment securities available-for-sale	6,839
After One Year Through Five Years [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	1,080
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	1,082
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	105,078
Available-for-Sale Market Value
Investment securities available-for-sale	103,623
After Five Years Through Ten Years [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	36,316
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	35,350
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	359,473
Available-for-Sale Market Value
Investment securities available-for-sale	336,171
After Ten Years [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	2,156
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	2,054
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	842,383
Available-for-Sale Market Value
Investment securities available-for-sale	765,553
Residential Mortgage Backed Securities [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	0	0
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	0	0
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	697,784	728,050
Available-for-Sale Market Value
Investment securities available-for-sale	627,752	724,137
Commercial Mortgage Backed Securities [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	38,327	46,362
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	35,786	47,013
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	762,091	729,948
Available-for-Sale Market Value
Investment securities available-for-sale	730,367	731,890
Collateralized Mortgage Backed Securities [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	10,178	11,882
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	9,718	12,103
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	556,531	696,258
Available-for-Sale Market Value
Investment securities available-for-sale	516,843	697,740
Asset-backed Securities [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	0	0
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	0	0
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	798,356	720,638
Available-for-Sale Market Value
Investment securities available-for-sale	$ 756,432	$ 719,581