INVESTMENT SECURITIES - Available-for-Sale Portfolio (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Available-for-Sale Portfolio
Amortized Cost	$ 3,871,881	$ 4,675,474
Gross Unrealized Gains	1,852	565
Gross Unrealized Losses	387,740	524,188
Total - Fair value	3,485,993	4,151,851
Held-to-Maturity Portfolio
Amortized Cost	1,090,235	1,079,695
Gross Unrealized Gains	93	0
Gross Unrealized Losses	6,998	44,900
Total - Fair Value	1,083,330	1,034,795
U.S. Treasury and agency securities
Available-for-Sale Portfolio
Amortized Cost	2,876,765	3,660,546
Gross Unrealized Gains	0	0
Gross Unrealized Losses	299,774	417,009
Total - Fair value	2,576,991	3,243,537
Held-to-Maturity Portfolio
Amortized Cost	1,086,936	1,079,695
Gross Unrealized Gains	78	0
Gross Unrealized Losses	6,983	44,900
Total - Fair Value	1,080,031	1,034,795
Obligations of state and political subdivisions
Available-for-Sale Portfolio
Amortized Cost	541,118	549,118
Gross Unrealized Gains	1,746	506
Gross Unrealized Losses	32,995	45,327
Total - Fair value	509,869	504,297
Government agency mortgage-backed securities
Available-for-Sale Portfolio
Amortized Cost	433,829	444,689
Gross Unrealized Gains	105	58
Gross Unrealized Losses	53,476	60,114
Total - Fair value	380,458	384,633
Held-to-Maturity Portfolio
Amortized Cost	3,299	0
Gross Unrealized Gains	15	0
Gross Unrealized Losses	15	0
Total - Fair Value	3,299	0
Corporate debt securities
Available-for-Sale Portfolio
Amortized Cost	8,000	8,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	810	886
Total - Fair value	7,190	7,114
Government agency collateralized mortgage obligations
Available-for-Sale Portfolio
Amortized Cost	12,169	13,121
Gross Unrealized Gains	1	1
Gross Unrealized Losses	685	852
Total - Fair value	11,485	$ 12,270
Held-to-Maturity Portfolio
Amortized Cost	0
Total - Fair Value	$ 0

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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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