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Note 2 - Securities (Details Textual) $ in Thousands | 12 Months Ended
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Dec. 31, 2024 USD ($) | Dec. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions | 843 | 641 |
Debt Securities, Available-for-Sale, Unrealized Loss Position | $ 680,417 | $ 548,747 |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss | 63,807 | 66,112 |
Proceeds from Sale of Debt Securities, Available-for-Sale | 0 | 0 | $ 0
Debt Securities, Available-for-Sale, Amortized Cost | 793,422 | 680,998 |
Debt Securities, Available-for-Sale | 730,352 | 617,092 |
Bonds Issued or Guaranteed by Agencies of the U.S. Federal Government [Member] |  |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss | 53,600 |  |
Bonds Issued by State-based Municipalities [Member] |  |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss | 10,200 |  |
State of Michigan and All Its Political Subdivisions [Member] |  |  |
Debt Securities, Available-for-Sale, Amortized Cost | 219,000 | 203,000 |
Debt Securities, Available-for-Sale | 209,000 | 197,000 |
All Other States and Their Political Subdivisions [Member] |  |  |
Debt Securities, Available-for-Sale, Amortized Cost | 0 | 0 |
US Government Agency Debt Obligations and Mortgage Backed Securities [Member] |  |  |
Debt Securities, Available-for-Sale, Restricted | 122,000 | 230,000 |
US Government Agencies Debt Securities [Member] |  |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position | 475,113 | 390,496 |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss | 47,226 | 52,000 |
Debt Securities, Available-for-Sale, Amortized Cost | 542,676 | 442,496 |
Debt Securities, Available-for-Sale | 495,581 | 390,496 |
Debt Securities, Available-for-Sale, Restricted | $ 11,700 | $ 0 |

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