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Note 2 - Securities (Details Textual)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	30	107
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 6,674,000	$ 117,573,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	25,000	1,254,000
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	306,080,000	329,979,000
Debt Securities, Available-for-sale, Total	312,147,000	334,655,000
State of Michigan and All Its Political Subdivisions [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	100,000,000	96,500,000
Debt Securities, Available-for-sale, Total	103,000,000	99,400,000
All Other States and Their Political Subdivisions [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	5,200,000	5,900,000
Debt Securities, Available-for-sale, Total	5,400,000	5,900,000
US Government Agency Debt Obligations and Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Restricted	$ 133,000,000	$ 103,000,000

X

- 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).

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