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INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Held-to-Maturity, Amortized Cost |  |
Due in one year or less | $ 0 |
Due after one through five years | 0 |
Due after five years through ten years | 552,838 |
Due after ten years | 556,263 |
Subtotal | 1,109,101 |
Total - Amortized Cost | 1,172,174 | $ 1,079,695
Held-to-Maturity, Fair Value |  |
Due in one year or less | 0 |
Due after one through five years | 0 |
Due after five years through ten years | 536,885 |
Due after ten years | 521,350 |
Subtotal | 1,058,235 |
Fair Value | 1,121,816 | 1,034,795
Available-for-Sale, Amortized Cost |  |
Due in one year or less | 16,671 |
Due after one through five years | 1,583,809 |
Due after five years through ten years | 579,092 |
Due after ten years | 712,475 |
Subtotal | 2,892,047 |
Amortized Cost | 3,301,607 | 4,675,474
Debt Securities, Available-for-Sale, Excluding Accrued Interest | 2,919,992 | 4,151,851
Available-for-Sale, Fair Value |  |
Due in one year or less | 16,566 |
Due after one through five years | 1,441,328 |
Due after five years through ten years | 523,830 |
Due after ten years | 580,816 |
Subtotal | 2,562,540 |
Government agency mortgage-backed securities |  |
Held-to-Maturity, Amortized Cost |  |
Total - Amortized Cost | 63,073 | 0
Held-to-Maturity, Fair Value |  |
Fair Value | 63,581 | 0
Available-for-Sale, Amortized Cost |  |
Amortized Cost | 400,062 | 444,689
Debt Securities, Available-for-Sale, Excluding Accrued Interest | 348,526 | 384,633
Government agency collateralized mortgage obligations |  |
Held-to-Maturity, Amortized Cost |  |
Total - Amortized Cost | 0 |
Held-to-Maturity, Fair Value |  |
Fair Value | 0 |
Available-for-Sale, Amortized Cost |  |
Amortized Cost | 9,498 | 13,121
Debt Securities, Available-for-Sale, Excluding Accrued Interest | 8,926 | 12,270
U.S. Treasury and agency securities |  |
Held-to-Maturity, Amortized Cost |  |
Total - Amortized Cost | 1,109,101 | 1,079,695
Held-to-Maturity, Fair Value |  |
Fair Value | 1,058,235 | 1,034,795
Available-for-Sale, Amortized Cost |  |
Amortized Cost | 2,381,168 | 3,660,546
Debt Securities, Available-for-Sale, Excluding Accrued Interest | $ 2,080,783 | $ 3,243,537

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