Note 2 - Investment Securities - Available-for-sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Securities available-for-sale, amortized cost	$ 1,123,119	$ 1,154,153
Securities available-for-sale, unrealized gains	168	245
Securities available-for-sale, unrealized losses	(129,479)	(123,219)
Securities available-for-sale, fair value	993,808	1,031,179
US Treasury Securities and US Government Agencies Debt Securities [Member]
Securities available-for-sale, amortized cost	119,955	119,931
Securities available-for-sale, unrealized gains	0	0
Securities available-for-sale, unrealized losses	(2,477)	(3,662)
Securities available-for-sale, fair value	117,478	116,269
US Government-sponsored Enterprises Debt Securities [Member]
Securities available-for-sale, amortized cost	96,057	104,677
Securities available-for-sale, unrealized gains	149	157
Securities available-for-sale, unrealized losses	(5,310)	(4,987)
Securities available-for-sale, fair value	90,896	99,847
Mortgage-Backed Security, Issued by US Government-Sponsored Enterprise [Member]
Securities available-for-sale, amortized cost	768,003	789,145
Securities available-for-sale, unrealized gains	16	83
Securities available-for-sale, unrealized losses	(107,399)	(101,189)
Securities available-for-sale, fair value	660,620	688,039
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale, amortized cost	135,318	136,579
Securities available-for-sale, unrealized gains	3	5
Securities available-for-sale, unrealized losses	(14,064)	(13,094)
Securities available-for-sale, fair value	121,257	123,490
Other Debt Obligations [Member]
Securities available-for-sale, amortized cost	3,786	3,821
Securities available-for-sale, unrealized gains	0	0
Securities available-for-sale, unrealized losses	(229)	(287)
Securities available-for-sale, fair value	$ 3,557	$ 3,534