Note 2 - Securities (Details Textual)	9 Months Ended	12 Months Ended
	Sep. 30, 2023 USD ($)	Dec. 31, 2022 USD ($)
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	809	732
Debt Securities, Available-for-Sale, Unrealized Loss Position	$ 585,698,000	$ 573,146,000
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	93,199,000	83,281,000
Proceeds from Sale of Debt Securities, Available-for-Sale	0	0
Debt Securities, Available-for-Sale, Amortized Cost	685,455,000	685,646,000
Debt Securities, Available-for-Sale	592,305,000	602,936,000
Bonds Issued or Guaranteed by Agencies of the U.S. Federal Government [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	75,900,000
Bonds Issued by State-based Municipalities [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	17,300,000
State of Michigan and All Its Political Subdivisions [Member]
Debt Securities, Available-for-Sale, Amortized Cost	197,000,000	193,000,000
Debt Securities, Available-for-Sale	180,000,000	182,000,000
All Other States and Their Political Subdivisions [Member]
Debt Securities, Available-for-Sale, Amortized Cost	0	0
US Government Agency Debt Obligations and Mortgage Backed Securities [Member]
Debt Securities, Available-for-Sale, Restricted	164,000,000	194,000,000
Deposit Liabilities, Collateral Issued, Financial Instruments	$ 96,500,000	$ 0