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INVESTMENT SECURITIES - Amortized Cost of Investment Securities Held to Maturity (Details) - USD ($) $ in Thousands | Sep. 30, 2023 | Dec. 31, 2022
--- | --- | ---
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | $ 2,213,833 | $ 2,287,372
Aaa |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 185,294 |
Aa1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 153,408 |
Aa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 181,369 |
Aa3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 133,499 |
A1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 131,310 |
A2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 10,172 |
A3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 10,125 |
Non-rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 1,408,656 |
State and municipal |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 1,107,325 | $ 1,117,552
State and municipal | Aaa |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 114,709 |
State and municipal | Aa1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 153,408 |
State and municipal | Aa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 181,369 |
State and municipal | Aa3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 133,499 |
State and municipal | A1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 131,310 |
State and municipal | A2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 10,172 |
State and municipal | A3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 10,125 |
State and municipal | Non-rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 372,733 |
Other |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 1,106,508 |
Other | Aaa |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 70,585 |
Other | Aa1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 0 |
Other | Aa2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 0 |
Other | Aa3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 0 |
Other | A1 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 0 |
Other | A2 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 0 |
Other | A3 |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | 0 |
Other | Non-rated |  |
Schedule of Held-to-maturity Securities [Line Items] |  |
Total | $ 1,035,923 |

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