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Note 2 - Securities (Details Textual) | Sep. 30, 2021 USD ($) | Dec. 31, 2020 USD ($)
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Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions | 291 |
Debt Securities, Available-for-sale, Unrealized Loss Position, Total | $ 390,206,000 | $ 119,073,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total | 5,956,000 | 899,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held, Ending Balance | 0 |
Debt Securities, Available-for-sale, Amortized Cost, Total | 559,938,000 | 380,403,000
Debt Securities, Available-for-sale, Total | 559,564,000 | 387,347,000
State of Michigan and All Its Political Subdivisions [Member] |  |
Debt Securities, Available-for-sale, Amortized Cost, Total | 148,000,000 | 109,000,000
Debt Securities, Available-for-sale, Total | 153,000,000 | 116,000,000
All Other States and Their Political Subdivisions [Member] |  |
Debt Securities, Available-for-sale, Amortized Cost, Total | 2,700,000 | 4,100,000
Debt Securities, Available-for-sale, Total | 2,700,000 | 4,200,000
US Government Agency Debt Obligations and Mortgage Backed Securities [Member] |  |
Debt Securities, Available-for-sale, Restricted | $ 176,000,000 | $ 118,000,000

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