INVESTMENTS - Summary of Investment Securities by Estimated Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Held-to-Maturity Amortized Cost
Amortized Cost	$ 85,823	$ 98,420
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	78,924	99,898
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	3,959,270	4,180,589
Available-for-Sale Market Value
Investment securities available-for-sale	3,531,353	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	13,484
Available-for-Sale Market Value
Investment securities available-for-sale	13,425
After One Year Through Five Years [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	1,088
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	1,052
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	106,451
Available-for-Sale Market Value
Investment securities available-for-sale	103,590
After Five Years Through Ten Years [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	36,362
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	34,202
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	306,244
Available-for-Sale Market Value
Investment securities available-for-sale	268,998
After Ten Years [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	1,967
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	1,814
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	801,835
Available-for-Sale Market Value
Investment securities available-for-sale	678,773
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	688,513	728,050
Available-for-Sale Market Value
Investment securities available-for-sale	586,292	724,137
Commercial Mortgage Backed Securities [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	36,714	46,362
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	32,956	47,013
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	731,619	729,948
Available-for-Sale Market Value
Investment securities available-for-sale	684,654	731,890
Collateralized Mortgage Backed Securities [Member]
Held-to-Maturity Amortized Cost
Amortized Cost	9,692	11,882
Held-to-Maturity Market Value
Debt Securities, Held-to-maturity, Fair Value	8,900	12,103
Available-for-Sale Amortized Cost
Debt Securities, Available-for-sale, Amortized Cost	550,209	696,258
Available-for-Sale Market Value
Investment securities available-for-sale	489,848	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	760,915	720,638
Available-for-Sale Market Value
Investment securities available-for-sale	$ 705,773	$ 719,581

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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