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Note 1 - Summary of Significant Accounting Policies (Details Textual)	3 Months Ended
	Mar. 31, 2021 USD ($) shares	Mar. 31, 2020 USD ($)	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
Impaired Financing Receivable, Recorded Investment, Total	10,389,000		$ 7,851,000
Stock Issued During Period, Value, New Issues	175,000	$ 106,000
Goodwill, Ending Balance	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
Goodwill, Purchase Accounting Adjustments	$ (560,000)
Directors' Stock Purchase Plan [Member]
Stock Issued During Period, Shares, New Issues (in shares) | shares	4,732
Stock Issued During Period, Value, New Issues	$ 146,000
Employee Stock Purchase Plan [Member]
Stock Issued During Period, Shares, New Issues (in shares) | shares	1,201
Stock Issued During Period, Value, New Issues	$ 29,000
Participating Interests in Mortgage Loans [Member]
Impaired Financing Receivable, Recorded Investment, Total	$ 0	$ 0
Credit Concentration Risk [Member] | Participating Interests in Mortgage Loans [Member]
Number Of Mortgage Bankers	14
Concentration Risk, Percentage	22.00%
Number of Participating Interest In Loans To Other Financial Institutions Over 30 Days	12		26
Number of Participating Interest In Loans To Other Financial Institutions	114		222
Participating Interest In Loans To Other Financial Institutions Over 30 Days	$ 2,100,000		$ 6,400,000

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