Note 2 - Securities (Details Textual)	3 Months Ended	12 Months Ended
	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	653	732
Debt Securities, Available-for-Sale, Unrealized Loss Position	$ 560,057,000	$ 573,146,000
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	72,527,000	83,281,000
Proceeds from Sale of Debt Securities, Available-for-Sale	0	0
Debt Securities, Available-for-Sale, Amortized Cost	691,197,000	685,646,000
Debt Securities, Available-for-Sale	619,973,000	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	63,400,000
Bonds Issued by State-based Municipalities [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	9,100,000
State of Michigan and All Its Political Subdivisions [Member]
Debt Securities, Available-for-Sale, Amortized Cost	200,000,000	193,000,000
Debt Securities, Available-for-Sale	192,000,000	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	$ 227,000,000	$ 194,000,000