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Note 2 - Securities (Details Textual) | 12 Months Ended
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Dec. 31, 2022 USD ($) | Dec. 31, 2021 USD ($) | Dec. 31, 2020 USD ($)
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions | 732 | 333 |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total | $ 573,146,000 | $ 461,553,000 |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss, Total | 83,281,000 | 9,958,000 |
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held | 0 | 0 |
Proceeds from Sale of Debt Securities, Available-for-Sale | 0 | 0 | $ 0
Debt Securities, Available-for-Sale, Amortized Cost, Total | 685,646,000 | 597,463,000 |
Debt Securities, Available-for-Sale, Total | 602,936,000 | 592,743,000 |
Bonds Issued or Guaranteed by Agencies of the U.S. Federal Government [Member] |  |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss, Total | 71,200,000 |  |
Bonds Issued by State-based Municipalities [Member] |  |  |
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss, Total | 12,100,000 |  |
State of Michigan and All Its Political Subdivisions [Member] |  |  |
Debt Securities, Available-for-Sale, Amortized Cost, Total | 193,000,000 | 155,000,000 |
Debt Securities, Available-for-Sale, Total | 182,000,000 | 158,000,000 |
All Other States and Their Political Subdivisions [Member] |  |  |
Debt Securities, Available-for-Sale, Amortized Cost, Total | 0 | 1,700,000 |
Debt Securities, Available-for-Sale, Total |  | 1,700,000 |
US Government Agency Debt Obligations and Mortgage Backed Securities [Member] |  |  |
Debt Securities, Available-for-Sale, Restricted | $ 194,000,000 | $ 197,000,000 |

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