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Note 3 - Debt Securities Available for Sale and Held to Maturity - Credit Quality (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Dec. 31, 2024
--- | --- | ---
Held to Maturity, Amortized Cost | $ 826,506 | $ 844,635
AAA/AA/A [Member] |  |
Held to Maturity, Amortized Cost | 642,875 |
BBB+/BBB [Member] |  |
Held to Maturity, Amortized Cost | 183,182 |
NR [Member] |  |
Held to Maturity, Amortized Cost | 449 |
Agency Residential MBS [Member] |  |
Held to Maturity, Amortized Cost | 46,433 | 57,927
Agency Residential MBS [Member] | AAA/AA/A [Member] |  |
Held to Maturity, Amortized Cost | 45,984 |
Agency Residential MBS [Member] | BBB+/BBB [Member] |  |
Held to Maturity, Amortized Cost | 0 |
Agency Residential MBS [Member] | NR [Member] |  |
Held to Maturity, Amortized Cost | 449 |
US States and Political Subdivisions Debt Securities [Member] |  |
Held to Maturity, Amortized Cost | 39,528 | 51,261
US States and Political Subdivisions Debt Securities [Member] | AAA/AA/A [Member] |  |
Held to Maturity, Amortized Cost | 39,528 |
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 | 740,545 | $ 735,447
Corporate Debt Securities [Member] | AAA/AA/A [Member] |  |
Held to Maturity, Amortized Cost | 557,363 |
Corporate Debt Securities [Member] | BBB+/BBB [Member] |  |
Held to Maturity, Amortized Cost | 183,182 |
Corporate Debt Securities [Member] | NR [Member] |  |
Held to Maturity, Amortized Cost | $ 0 |

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- Definition Amount excluding accrued interest, before allowance for credit loss, of investment in debt security measured at amortized cost (held-to-maturity). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147479344/326-20-45-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3B -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-3B Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 5 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147479319/326-20-50-5 + Details
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