Note 2 - Securities (Details Textual)	12 Months Ended
	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	333
Debt Securities, Available-for-sale, Unrealized Loss Position, Total	$ 461,553,000	$ 119,073,000
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss, Total	9,958,000	899,000
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Credit Losses on Debt Securities Held, Ending Balance	0
Proceeds from Sale of Debt Securities, Available-for-sale	0	0	$ 0
Debt Securities, Available-for-sale, Amortized Cost, Total	597,463,000	380,403,000
Debt Securities, Available-for-sale, Total	592,743,000	387,347,000
State of Michigan and All Its Political Subdivisions [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	155,000,000	109,000,000
Debt Securities, Available-for-sale, Total	158,000,000	116,000,000
All Other States and Their Political Subdivisions [Member]
Debt Securities, Available-for-sale, Amortized Cost, Total	1,700,000	4,100,000
Debt Securities, Available-for-sale, Total	1,700,000	4,200,000
US Government Agency Debt Obligations and Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale, Restricted	$ 197,000,000	$ 118,000,000