Note 3 - Investment Securities - Securities in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Temporarily impaired securities, fair value	$ 551,786	$ 608,473
Temporarily impaired securities, unrealized losses	(82,424)	(87,204)
Temporarily impaired securities, fair value, less than 12 months	10,160	307,425
Temporarily impaired securities, unrealized losses, less than 12 months	(130)	(21,450)
Temporarily impaired securities, fair value, 12 months or longer	541,626	301,048
Temporarily impaired securities, unrealized losses, 12 months or longer	(82,294)	(65,754)
US Government Agencies Debt Securities [Member]
Temporarily impaired securities, fair value	40,779	44,451
Temporarily impaired securities, unrealized losses	(10,761)	(10,439)
Temporarily impaired securities, fair value, less than 12 months	1,689	20,517
Temporarily impaired securities, unrealized losses, less than 12 months	(65)	(1,831)
Temporarily impaired securities, fair value, 12 months or longer	39,090	23,934
Temporarily impaired securities, unrealized losses, 12 months or longer	(10,696)	(8,608)
Residential Mortgage-Backed Securities [Member]
Temporarily impaired securities, fair value	382,042	403,039
Temporarily impaired securities, unrealized losses	(51,433)	(57,863)
Temporarily impaired securities, fair value, less than 12 months	4,138	218,918
Temporarily impaired securities, unrealized losses, less than 12 months	(51)	(13,869)
Temporarily impaired securities, fair value, 12 months or longer	377,904	184,121
Temporarily impaired securities, unrealized losses, 12 months or longer	(51,382)	(43,994)
Commercial Mortgage-Backed Securities [Member]
Temporarily impaired securities, fair value	21,565	21,105
Temporarily impaired securities, unrealized losses	(3,676)	(4,381)
Temporarily impaired securities, fair value, less than 12 months	0	14,523
Temporarily impaired securities, unrealized losses, less than 12 months	0	(2,304)
Temporarily impaired securities, fair value, 12 months or longer	21,565	6,582
Temporarily impaired securities, unrealized losses, 12 months or longer	(3,676)	(2,077)
US States and Political Subdivisions Debt Securities [Member]
Temporarily impaired securities, fair value	101,189	133,265
Temporarily impaired securities, unrealized losses	(16,505)	(14,462)
Temporarily impaired securities, fair value, less than 12 months	1,340	47,446
Temporarily impaired securities, unrealized losses, less than 12 months	(7)	(3,404)
Temporarily impaired securities, fair value, 12 months or longer	99,849	85,819
Temporarily impaired securities, unrealized losses, 12 months or longer	(16,498)	(11,058)
Corporate Debt Securities [Member]
Temporarily impaired securities, fair value	4,973	4,973
Temporarily impaired securities, unrealized losses	(27)	(26)
Temporarily impaired securities, fair value, less than 12 months	2,993	4,973
Temporarily impaired securities, unrealized losses, less than 12 months	(7)	(26)
Temporarily impaired securities, fair value, 12 months or longer	1,980	0
Temporarily impaired securities, unrealized losses, 12 months or longer	(20)	0
Asset-Backed Securities [Member]
Temporarily impaired securities, fair value	1,238	1,640
Temporarily impaired securities, unrealized losses	(22)	(33)
Temporarily impaired securities, fair value, less than 12 months	0	1,048
Temporarily impaired securities, unrealized losses, less than 12 months	0	(16)
Temporarily impaired securities, fair value, 12 months or longer	1,238	592
Temporarily impaired securities, unrealized losses, 12 months or longer	$ (22)	$ (17)