Note 6 - Debt Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Jun. 30, 2022 USD ($) security	Dec. 31, 2021 USD ($) security
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	589	266
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 466,694	$ 463,870
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(55,307)	(6,923)
Debt Securities in an unrealized loss position 12 months or longer, fair value	131,166	44,155
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(22,597)	(1,379)
Debt Securities in an unrealized loss position, fair value	597,860	508,025
Debt Securities in an unrealized loss position, unrealized losses	$ (77,904)	$ (8,302)
US Treasury Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	2
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 594
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(2)
Debt Securities in an unrealized loss position, fair value	594
Debt Securities in an unrealized loss position, unrealized losses	$ (2)
US Government Agencies Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	46	44
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 34,585	$ 62,530
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(3,360)	(1,407)
Debt Securities in an unrealized loss position 12 months or longer, fair value	56,506	32,968
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(7,487)	(1,028)
Debt Securities in an unrealized loss position, fair value	91,091	95,498
Debt Securities in an unrealized loss position, unrealized losses	$ (10,847)	$ (2,435)
US States and Political Subdivisions Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	222	103
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 80,827	$ 55,982
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(14,370)	(953)
Debt Securities in an unrealized loss position 12 months or longer, fair value	20,337	3,742
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(6,688)	(100)
Debt Securities in an unrealized loss position, fair value	101,164	59,724
Debt Securities in an unrealized loss position, unrealized losses	$ (21,058)	$ (1,053)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	190	72
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 242,311	$ 253,141
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(27,518)	(2,915)
Debt Securities in an unrealized loss position 12 months or longer, fair value	42,163	7,370
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(6,609)	(243)
Debt Securities in an unrealized loss position, fair value	284,474	260,511
Debt Securities in an unrealized loss position, unrealized losses	$ (34,127)	$ (3,158)
Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	126	46
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 104,970	$ 92,217
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(9,863)	(1,648)
Debt Securities in an unrealized loss position 12 months or longer, fair value	12,105
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(1,806)
Debt Securities in an unrealized loss position, fair value	117,075	92,217
Debt Securities in an unrealized loss position, unrealized losses	$ (11,669)	$ (1,648)
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	3	1
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 3,407
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(194)
Debt Securities in an unrealized loss position 12 months or longer, fair value	55	$ 75
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(7)	(8)
Debt Securities in an unrealized loss position, fair value	3,462	75
Debt Securities in an unrealized loss position, unrealized losses	$ (201)	$ (8)