| **INVESTMENT SECURITIES - Contractual Maturity of HTM Debt Securities (Details) - USD ($) $ in Thousands** | Dec. 31, 2023 | Dec. 31, 2022 |
|------------------------------------------------------------------------------------------------------------|---------------|---------------|
| **Fair Value**                                                                                             |          |          |
| Due Within One Year                                                                                        | $ 0           |          |
| Due after 1 year but within 5 years                                                                   | 27,022        |          |
| Due after 5 years but within 10 years                                                                 | 6,863         |          |
| Due after 10 years                                                                                    | 7,528,638     |          |
| Total                                                                                                      | $ 7,562,523   | $ 8,273,285   |
| **Weighted average yield**                                                                                 |          |          |
| Due Within One Year                                                                                        | 0.00%         |          |
| Due After 1 Within 5 Years                                                                                 | 1.84%         |          |
| Due After 5 Within 10 Years                                                                                | 3.94%         |          |
| Due After 10 Years/No Maturity                                                                             | 2.38%         |          |
| Weighted average yield                                                                                     | 2.38%         |          |
| **Amortized Cost**                                                                                         |          |          |
| Due Within One Year                                                                                        | $ 0           |          |
| Due after 1 year but within 5 years                                                                   | 27,384        |          |
| Due after 5 years but within 10 years                                                                 | 7,077         |          |
| Due after 10 years                                                                                    | 9,005,243     |          |
| Total                                                                                                      | 9,039,704     |          |
| ABS                                                                                                        |          |          |
| **Fair Value**                                                                                             |          |          |
| Due Within One Year                                                                                        | 0             |          |
| Due after 1 year but within 5 years                                                                   | 27,022        |          |
| Due after 5 years but within 10 years                                                                 | 2,316         |          |
| Due after 10 years                                                                                    | 0             |          |
| Total                                                                                                      | $ 29,338      | 51,234        |
| **Weighted average yield**                                                                                 |          |          |
| Weighted average yield                                                                                     | 2.30%         |          |
| GNMA - Residential                                                                                         |          |          |
| **Fair Value**                                                                                             |          |          |
| Due Within One Year                                                                                        | $ 0           |          |
| Due after 1 year but within 5 years                                                                   | 0             |          |
| Due after 5 years but within 10 years                                                                 | 4,547         |          |
| Due after 10 years                                                                                    | 2,278,406     |          |
| Total                                                                                                      | $ 2,282,953   | 2,476,878     |
| **Weighted average yield**                                                                                 |          |          |
| Weighted average yield                                                                                     | 2.41%         |          |
| GNMA - Commercial                                                                                          |          |          |
| **Fair Value**                                                                                             |          |          |
| Due Within One Year                                                                                        | $ 0           |          |
| Due after 1 year but within 5 years                                                                   | 0             |          |
| Due after 5 years but within 10 years                                                                 | 0             |          |
| Due after 10 years                                                                                    | 3,949,335     |          |
| Total                                                                                                      | $ 3,949,335   | 4,333,521     |
| **Weighted average yield**                                                                                 |          |          |
| Weighted average yield                                                                                     | 2.29%         |          |
| FHLMC and FNMA - Residential                                                                               |          |          |
| **Fair Value**                                                                                             |          |          |
| Due Within One Year                                                                                        | $ 0           |          |
| Due after 1 year but within 5 years                                                                   | 0             |          |
| Due after 5 years but within 10 years                                                                 | 0             |          |
| Due after 10 years                                                                                    | 1,300,897     |          |
| Total                                                                                                      | $ 1,300,897   | $ 1,411,652   |
| **Weighted average yield**                                                                                 |          |          |
| Weighted average yield                                                                                     | 2.58%         |          |

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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Amount excluding accrued interest, after allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity) with single maturity date and allocated without single maturity date.
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Amount excluding accrued interest, after allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity) with single maturity date and allocated without single maturity date, maturing after tenth 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).
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| - Definition
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| - Definition
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| - Definition
Weighted average yield of investment in debt security measured at amortized cost (held-to-maturity) maturing after tenth 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).
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