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INVESTMENT SECURITIES - Amortized Cost and Estimated Fair Value of Debt Securities by Contractual Maturity (Details) - USD ($) $ in Thousands | Mar. 31, 2024 | Dec. 31, 2023
--- | --- | ---
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 | 556,091 |
Due after ten years | 560,367 |
Subtotal | 1,116,458 |
Total - Amortized Cost | 1,217,472 | $ 1,172,174
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 | 527,314 |
Due after ten years | 503,684 |
Subtotal | 1,030,998 |
Fair Value | 1,131,615 | 1,121,816
Available-for-Sale, Amortized Cost |  |
Due in one year or less | 14,764 |
Due after one through five years | 1,682,697 |
Due after five years through ten years | 492,385 |
Due after ten years | 697,790 |
Subtotal | 2,887,636 |
Amortized Cost | 3,287,497 | 3,301,607
Fair Value | 2,863,864 | 2,919,992
Available-for-Sale, Fair Value |  |
Due in one year or less | 14,603 |
Due after one through five years | 1,517,578 |
Due after five years through ten years | 438,082 |
Due after ten years | 552,843 |
Subtotal | 2,523,106 |
Government agency mortgage-backed securities |  |
Held-to-Maturity, Amortized Cost |  |
Total - Amortized Cost | 101,014 | 63,073
Held-to-Maturity, Fair Value |  |
Fair Value | 100,617 | 63,581
Available-for-Sale, Amortized Cost |  |
Amortized Cost | 391,020 | 400,062
Fair Value | 332,479 | 348,526
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 | 8,841 | 9,498
Fair Value | 8,279 | 8,926
U.S. Treasury and agency securities |  |
Held-to-Maturity, Amortized Cost |  |
Total - Amortized Cost | 1,116,458 | 1,109,101
Held-to-Maturity, Fair Value |  |
Fair Value | 1,030,998 | 1,058,235
Available-for-Sale, Amortized Cost |  |
Amortized Cost | 2,382,653 | 2,381,168
Fair Value | $ 2,055,517 | $ 2,080,783

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- Definition Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), with single maturity date and allocated without single maturity date, maturing in second through fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 320 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147481800/320-10-50-3 + Details
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