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Note 2 - Securities (Details Textual) | Mar. 31, 2022 USD ($) | Dec. 31, 2021 USD ($)
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Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions | 527 | 333
Debt Securities, Available-for-Sale, Unrealized Loss Position, Total | $ 534,729,000 | $ 461,553,000
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss, Total | 41,146,000 | 9,958,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held | 0 | 0
Debt Securities, Available-for-Sale, Amortized Cost, Total | 646,031,000 | 597,463,000
Debt Securities, Available-for-Sale, Total | 605,661,000 | 592,743,000
State of Michigan and All Its Political Subdivisions [Member] |  |
Debt Securities, Available-for-Sale, Amortized Cost, Total | 161,000,000 | 155,000,000
Debt Securities, Available-for-Sale, Total | 155,000,000 | 158,000,000
All Other States and Their Political Subdivisions [Member] |  |
Debt Securities, Available-for-Sale, Amortized Cost, Total | 1,600,000 | 1,700,000
Debt Securities, Available-for-Sale, Total | 1,600,000 | 1,700,000
US Government Agency Debt Obligations and Mortgage Backed Securities [Member] |  |
Debt Securities, Available-for-Sale, Restricted | $ 204,000,000 | $ 197,000,000

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- Definition Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 30 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454 + Details
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