Note 2 - Investment Securities - Held to Maturity Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Securities held-to-maturity, carrying value	$ 450,029		$ 473,217
Securities held-to-maturity, gains	0		0
Securities held-to-maturity, losses	(39,780)		(41,384)
Securities held-to-maturity, fair value	410,249	$ 410,249	431,833
US Treasury Securities and US Government Agencies Debt Securities [Member]
Securities held-to-maturity, carrying value	204,017		217,794
Securities held-to-maturity, gains	0		0
Securities held-to-maturity, losses	(8,678)		(9,166)
Securities held-to-maturity, fair value	195,339		208,628
US Government-sponsored Enterprises Debt Securities [Member]
Securities held-to-maturity, carrying value	27,127		27,507
Securities held-to-maturity, gains	0		0
Securities held-to-maturity, losses	(2,955)		(2,559)
Securities held-to-maturity, fair value	24,172		24,948
Mortgage-Backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities held-to-maturity, carrying value	218,885		227,916
Securities held-to-maturity, gains	0		0
Securities held-to-maturity, losses	(28,147)		(29,659)
Securities held-to-maturity, fair value	$ 190,738		$ 198,257