Note 6 - Fair Value of Financial Instruments (Details Textual)	3 Months Ended	12 Months Ended
Mar. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)
Debt Securities, Available-for-Sale	$ 615,350,000	$ 624,779,000
Fair Value, Recurring [Member]
Debt Securities, Available-for-Sale	615,350,000	624,779,000
Assets, Fair Value Disclosure	616,223,000	626,053,000
Fair Value, Nonrecurring [Member]
Assets, Fair Value Disclosure	0	0
Fair Value, Inputs, Level 3 [Member] \| Fair Value, Recurring [Member]
Debt Securities, Available-for-Sale	116,000	136,000
Assets, Fair Value Disclosure	$ 116,000	$ 136,000
US States and Political Subdivisions Debt Securities [Member] \| Fair Value, Inputs, Level 3 [Member] \| Fair Value, Recurring [Member]
Number Of Non-Rated Bond Anticipation Notes	3
Debt Securities, Available-for-Sale	$ 116,000
Debt Securities, Maturity Period (Year)		1 year

Amount 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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+ Details