Note 3 - Securities (Details Textual)	12 Months Ended
Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	107
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 117,573,000	$ 278,331,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	1,254,000	11,357,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held, Ending Balance	0
Proceeds from Sale of Available-for-sale Securities, Total	0	0	$ 7,619,000
Debt Securities, Available-for-sale, Amortized Cost, Total	329,979,000	347,795,000
Debt Securities, Available-for-sale, Total	334,655,000	337,366,000
Collateralized Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	13,261,000	35,222,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	82,000	792,000
Proceeds from Sale of Available-for-sale Securities, Total	0	0	5,000,000
Debt Securities, Available-for-sale, Amortized Cost, Total	41,998,000	44,263,000
Debt Securities, Available-for-sale, Total	42,470,000	43,658,000
Municipal General Obligation Bonds [Member]
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	4,749,000	72,884,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	30,000	1,165,000
Proceeds from Sale of Available-for-sale Securities, Total	0	0	$ 2,600,000
Debt Securities, Available-for-sale, Amortized Cost, Total	98,245,000	103,235,000
Debt Securities, Available-for-sale, Total	101,079,000	102,497,000
State of Michigan and All Its Political Subdivisions [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	96,500,000	98,200,000
Debt Securities, Available-for-sale, Total	99,400,000	97,400,000
All Other States and Their Political Subdivisions [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	5,900,000	8,700,000
Debt Securities, Available-for-sale, Total	5,900,000	8,700,000
US Government Agency Debt Obligations and Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Restricted	$ 103,000,000	$ 104,000,000

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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