Note 3 - Investment Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Securities available-for-sale, amortized cost	$ 1,266,356	$ 1,297,977
Securities available-for-sale, unrealized gains	75	349
Securities available-for-sale, unrealized losses	(134,579)	(153,709)
Securities available-for-sale, fair value	1,131,852	1,144,617
US Treasury Securities and US Government Agencies Debt Securities [Member]
Securities available-for-sale, amortized cost	122,752	122,966
Securities available-for-sale, unrealized gains	0	0
Securities available-for-sale, unrealized losses	(6,464)	(7,927)
Securities available-for-sale, fair value	116,288	115,039
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, amortized cost	142,900	149,773
Securities available-for-sale, unrealized gains	75	290
Securities available-for-sale, unrealized losses	(5,196)	(6,437)
Securities available-for-sale, fair value	137,779	143,626
Mortgage-Backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities available-for-sale, amortized cost	851,879	874,265
Securities available-for-sale, unrealized gains	0	58
Securities available-for-sale, unrealized losses	(108,424)	(121,585)
Securities available-for-sale, fair value	743,455	752,738
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale, amortized cost	142,901	145,016
Securities available-for-sale, unrealized gains	0	1
Securities available-for-sale, unrealized losses	(14,176)	(17,418)
Securities available-for-sale, fair value	128,725	127,599
Other Debt Obligations [Member]
Securities available-for-sale, amortized cost	5,924	5,957
Securities available-for-sale, unrealized gains	0	0
Securities available-for-sale, unrealized losses	(319)	(342)
Securities available-for-sale, fair value	$ 5,605	$ 5,615