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Note 3 - Investment Securities - Credit Quality (Details) - USD ($) $ in Thousands | Mar. 31, 2025 | Dec. 31, 2024
--- | --- | ---
Held to Maturity, Amortized Cost | $ 839,349 | $ 844,635
AAA/AA/A [Member] |  |
Held to Maturity, Amortized Cost | 656,610 |
BBB+/BBB [Member] |  |
Held to Maturity, Amortized Cost | 182,275 |
NR [Member] |  |
Held to Maturity, Amortized Cost | 464 |
Agency Residential MBS [Member] |  |
Held to Maturity, Amortized Cost | 53,528 | 57,927
Agency Residential MBS [Member] | AAA/AA/A [Member] |  |
Held to Maturity, Amortized Cost | 53,064 |
Agency Residential MBS [Member] | BBB+/BBB [Member] |  |
Held to Maturity, Amortized Cost | 0 |
Agency Residential MBS [Member] | NR [Member] |  |
Held to Maturity, Amortized Cost | 464 |
US States and Political Subdivisions Debt Securities [Member] |  |
Held to Maturity, Amortized Cost | 48,675 | 51,261
US States and Political Subdivisions Debt Securities [Member] | AAA/AA/A [Member] |  |
Held to Maturity, Amortized Cost | 48,675 |
US States and Political Subdivisions Debt Securities [Member] | BBB+/BBB [Member] |  |
Held to Maturity, Amortized Cost | 0 |
US States and Political Subdivisions Debt Securities [Member] | NR [Member] |  |
Held to Maturity, Amortized Cost | 0 |
Corporate Debt Securities [Member] |  |
Held to Maturity, Amortized Cost | 737,146 | $ 735,447
Corporate Debt Securities [Member] | AAA/AA/A [Member] |  |
Held to Maturity, Amortized Cost | 554,871 |
Corporate Debt Securities [Member] | BBB+/BBB [Member] |  |
Held to Maturity, Amortized Cost | 182,275 |
Corporate Debt Securities [Member] | NR [Member] |  |
Held to Maturity, Amortized Cost | $ 0 |

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