Note 2 - Securities (Details Textual) $ in Thousands	12 Months Ended
Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	641	732
Debt Securities, Available-for-Sale, Unrealized Loss Position	$ 548,747	$ 573,146
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	66,112	83,281
Proceeds from Sale of Debt Securities, Available-for-Sale	0	0	$ 0
Debt Securities, Available-for-Sale, Amortized Cost	680,998	685,646
Debt Securities, Available-for-Sale	617,092	602,936
Bonds Issued or Guaranteed by Agencies of the U.S. Federal Government [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	57,700
Bonds Issued by State-based Municipalities [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	8,400
State of Michigan and All Its Political Subdivisions [Member]
Debt Securities, Available-for-Sale, Amortized Cost	203,000	193,000
Debt Securities, Available-for-Sale	197,000	182,000
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	$ 230,000	$ 194,000

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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