Note 2 - Securities (Details Textual) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	799	843
Debt Securities, Available-for-Sale, Unrealized Loss Position	$ 639,943	$ 680,417
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	53,467	63,807
Proceeds from Sale of Debt Securities, Available-for-Sale	0	0
Debt Securities, Available-for-Sale, Amortized Cost	839,060	793,422
Debt Securities, Available-for-Sale	787,583	730,352
Bonds Issued or Guaranteed by Agencies of the U.S. Federal Government [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	43,400
Bonds Issued by State-based Municipalities [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	10,100
State of Michigan and All Its Political Subdivisions [Member]
Debt Securities, Available-for-Sale, Amortized Cost	224,000	219,000
Debt Securities, Available-for-Sale	215,000	209,000
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	242,000	122,000
US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-Sale, Unrealized Loss Position	437,830	475,113
Debt Securities, Available-for-Sale, Unrealized Loss Position, Accumulated Loss	37,703	47,226
Debt Securities, Available-for-Sale, Amortized Cost	583,732	542,676
Debt Securities, Available-for-Sale	547,409	495,581
Debt Securities, Available-for-Sale, Restricted	$ 12,100	$ 11,700

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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