Note 6 - Fair Value of Financial Instruments (Details Textual)	9 Months Ended
	Sep. 30, 2024 USD ($)	Dec. 31, 2023 USD ($)
Debt Securities, Available-for-Sale	$ 659,696,000	$ 695,877,000
Fair Value, Recurring [Member]
Debt Securities, Available-for-Sale	659,696,000	695,877,000
Assets, Fair Value Disclosure	660,114,000	696,459,000
Fair Value, Recurring [Member] \| Premises And Facilities [Member]
Assets, Fair Value Disclosure	383,000
Fair Value, Inputs, Level 3 [Member] \| Fair Value, Recurring [Member]
Debt Securities, Available-for-Sale	136,000	192,000
Assets, Fair Value Disclosure	$ 136,000	$ 192,000
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	$ 136,000
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

FIRST OF LONG ISLAND CORP 10-Q