Note 3 - Investment Securities (Details Textual) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022	Sep. 30, 2022	Dec. 31, 2021
Debt Securities, Held-to-Maturity, Allowance for Credit Loss	$ 1	$ 1	$ 7	$ 7
Debt Securities, Available-for-Sale and Held-to-Maturity, Before Allowance for Credit Loss	4,724,628	5,205,254
Asset Pledged as Collateral [Member] | Public Deposits and Short-term Borrowed Funds [Member]
Debt Securities, Available-for-Sale and Held-to-Maturity, Before Allowance for Credit Loss	$ 1,962,357	$ 1,180,010