Note 3 - Investment Securities - Securities in an Unrealized Loss Position (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Temporarily impaired securities, fair value	$ 591,193	$ 608,473
Temporarily impaired securities, unrealized losses	(80,965)	(87,204)
Temporarily impaired securities, fair value, less than 12 months	191,808	307,425
Temporarily impaired securities, unrealized losses, less than 12 months	(6,534)	(21,450)
Temporarily impaired securities, fair value, 12 months or longer	399,385	301,048
Temporarily impaired securities, unrealized losses, 12 months or longer	(74,431)	(65,754)
US Government Agencies Debt Securities [Member]
Temporarily impaired securities, fair value	43,301	44,451
Temporarily impaired securities, unrealized losses	(9,787)	(10,439)
Temporarily impaired securities, fair value, less than 12 months	2,798	20,517
Temporarily impaired securities, unrealized losses, less than 12 months	(209)	(1,831)
Temporarily impaired securities, fair value, 12 months or longer	40,503	23,934
Temporarily impaired securities, unrealized losses, 12 months or longer	(9,578)	(8,608)
Residential Mortgage-Backed Securities [Member]
Temporarily impaired securities, fair value	404,073	403,039
Temporarily impaired securities, unrealized losses	(50,580)	(57,863)
Temporarily impaired securities, fair value, less than 12 months	153,706	218,918
Temporarily impaired securities, unrealized losses, less than 12 months	(4,627)	(13,869)
Temporarily impaired securities, fair value, 12 months or longer	250,367	184,121
Temporarily impaired securities, unrealized losses, 12 months or longer	(45,953)	(43,994)
Commercial Mortgage-Backed Securities [Member]
Temporarily impaired securities, fair value	21,960	21,105
Temporarily impaired securities, unrealized losses	(3,464)	(4,381)
Temporarily impaired securities, fair value, less than 12 months	6,540	14,523
Temporarily impaired securities, unrealized losses, less than 12 months	(460)	(2,304)
Temporarily impaired securities, fair value, 12 months or longer	15,420	6,582
Temporarily impaired securities, unrealized losses, 12 months or longer	(3,004)	(2,077)
US States and Political Subdivisions Debt Securities [Member]
Temporarily impaired securities, fair value	118,428	133,265
Temporarily impaired securities, unrealized losses	(17,060)	(14,462)
Temporarily impaired securities, fair value, less than 12 months	26,397	47,446
Temporarily impaired securities, unrealized losses, less than 12 months	(1,194)	(3,404)
Temporarily impaired securities, fair value, 12 months or longer	92,031	85,819
Temporarily impaired securities, unrealized losses, 12 months or longer	(15,866)	(11,058)
Corporate Debt Securities [Member]
Temporarily impaired securities, fair value	1,977	4,973
Temporarily impaired securities, unrealized losses	(23)	(26)
Temporarily impaired securities, fair value, less than 12 months	1,977	4,973
Temporarily impaired securities, unrealized losses, less than 12 months	(23)	(26)
Temporarily impaired securities, fair value, 12 months or longer	0	0
Temporarily impaired securities, unrealized losses, 12 months or longer	0	0
Asset-Backed Securities [Member]
Temporarily impaired securities, fair value	1,454	1,640
Temporarily impaired securities, unrealized losses	(51)	(33)
Temporarily impaired securities, fair value, less than 12 months	390	1,048
Temporarily impaired securities, unrealized losses, less than 12 months	(21)	(16)
Temporarily impaired securities, fair value, 12 months or longer	1,064	592
Temporarily impaired securities, unrealized losses, 12 months or longer	$ (30)	$ (17)