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Note 1 - Summary of Significant Accounting Policies (Details Textual) | 3 Months Ended | 9 Months Ended |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2021 USD ($) | Mar. 31, 2021 | Sep. 30, 2020 USD ($) | Sep. 30, 2021 USD ($) $ / shares shares | Sep. 30, 2020 USD ($) | Apr. 30, 2021 shares | Dec. 31, 2020 USD ($) | Jul. 01, 2020 USD ($) | Dec. 31, 2019 USD ($) | Oct. 01, 2019 USD ($) | Dec. 31, 2006 USD ($)
Participating Interest In Loans, Losses or Charge-offs |  |  |  | $ 0 | $ 0 |  |  |  |  |  |
Stock Issued During Period, Value, New Issues | $ 139,000 |  | $ 143,000 | $ 420,000 | $ 304,000 |  |  |  |  |  |
Stock Repurchased During Period, Shares (in shares) | shares |  |  |  | 223,000 |  |  |  |  |  |  |
Stock Repurchased During Period, Value | 2,664,000 |  |  | $ 5,561,000 |  |  |  |  |  |  |
Stock Repurchased, Price Per Share (in dollars per share) | $ / shares |  |  |  | $ 24.94 |  |  |  |  |  |  |
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares) | shares |  |  |  |  |  | 390,114 |  |  |  |  |
Stock Repurchase Program, Percent of Stock Outstanding |  |  |  |  |  | 5.00% |  |  |  |  |
Goodwill, Ending Balance | $ 59,946,000 |  |  | $ 59,946,000 |  |  | $ 60,506,000 |  |  |  |
Valley Ridge Financial Corp. [Member] |  |  |  |  |  |  |  |  |  |  |
Goodwill, Ending Balance |  |  |  |  |  |  |  |  |  |  | $ 13,700,000
County Bank Corp ("County") [Member] |  |  |  |  |  |  |  |  |  |  |
Goodwill, Ending Balance |  |  |  |  |  |  |  |  | $ 38,900,000 | $ 38,866,000 |
Community Shores Bank Corp ("Community Shores") [Member] |  |  |  |  |  |  |  |  |  |  |
Goodwill, Ending Balance |  |  |  |  |  |  | $ 7,300,000 | $ 7,353,000 |  |  |
Directors' Stock Purchase Plan [Member] |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues (in shares) | shares |  |  |  | 13,092 |  |  |  |  |  |  |
Stock Issued During Period, Value, New Issues |  |  |  | $ 348,000 |  |  |  |  |  |  |
Employee Stock Purchase Plan [Member] |  |  |  |  |  |  |  |  |  |  |
Stock Issued During Period, Shares, New Issues (in shares) | shares |  |  |  | 4,718 |  |  |  |  |  |  |
Stock Issued During Period, Value, New Issues |  |  |  | $ 104,000 |  |  |  |  |  |  |
Participating Interests in Mortgage Loans [Member] | Credit Concentration Risk [Member] |  |  |  |  |  |  |  |  |  |  |
Number Of Mortgage Bankers |  | 11 |  |  |  |  |  |  |  |  |
Number of Participating Interest In Loans To Other Financial Institutions Over 30 Days | 0 |  |  | 0 |  |  | 26 |  |  |  |
Number of Participating Interest In Loans To Other Financial Institutions |  |  |  |  |  |  | 218 |  |  |  |
Participating Interests in Mortgage Loans [Member] | Credit Concentration Risk [Member] | Past Due 30 Days or More [Member] |  |  |  |  |  |  |  |  |  |  |
Participating Mortgage Loans, Mortgage Obligations, Amount |  |  |  |  |  |  | $ 7,900,000 |  |  |  |
Participating Interests in Mortgage Loans [Member] | Credit Concentration Risk [Member] | Eleven Mortgage Brokers [Member] |  |  |  |  |  |  |  |  |  |  |
Concentration Risk, Percentage |  | 17.00% |  |  |  |  |  |  |  |  |

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