Note 2 - Securities (Details Textual) $ in Thousands	12 Months Ended
Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	843	641
Debt Securities, Available-for-Sale, Unrealized Loss Position	$ 680,417	$ 548,747
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	63,807	66,112
Proceeds from Sale of Debt Securities, Available-for-Sale	0	0	$ 0
Debt Securities, Available-for-Sale, Amortized Cost	793,422	680,998
Debt Securities, Available-for-Sale	730,352	617,092
Bonds Issued or Guaranteed by Agencies of the U.S. Federal Government [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	53,600
Bonds Issued by State-based Municipalities [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	10,200
State of Michigan and All Its Political Subdivisions [Member]
Debt Securities, Available-for-Sale, Amortized Cost	219,000	203,000
Debt Securities, Available-for-Sale	209,000	197,000
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	122,000	230,000
US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position	475,113	390,496
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	47,226	52,000
Debt Securities, Available-for-Sale, Amortized Cost	542,676	442,496
Debt Securities, Available-for-Sale	495,581	390,496
Debt Securities, Available-for-Sale, Restricted	$ 11,700	$ 0

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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