Note 6 - Debt Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Mar. 31, 2022 USD ($) security	Dec. 31, 2021 USD ($) security
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	537	266
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 485,998	$ 463,870
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(37,325)	(6,923)
Debt Securities in an unrealized loss position 12 months or longer, fair value	126,709	44,155
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(14,012)	(1,379)
Debt Securities in an unrealized loss position, fair value	612,707	508,025
Debt Securities in an unrealized loss position, unrealized losses	$ (51,337)	$ (8,302)
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	$ 35,508	$ 62,530
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(2,434)	(1,407)
Debt Securities in an unrealized loss position 12 months or longer, fair value	58,554	32,968
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(5,438)	(1,028)
Debt Securities in an unrealized loss position, fair value	94,062	95,498
Debt Securities in an unrealized loss position, unrealized losses	$ (7,872)	$ (2,435)
US States and Political Subdivisions Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	190	103
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 75,613	$ 55,982
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(8,712)	(953)
Debt Securities in an unrealized loss position 12 months or longer, fair value	19,860	3,742
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(3,715)	(100)
Debt Securities in an unrealized loss position, fair value	95,473	59,724
Debt Securities in an unrealized loss position, unrealized losses	$ (12,427)	$ (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	178	72
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 256,078	$ 253,141
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(18,096)	(2,915)
Debt Securities in an unrealized loss position 12 months or longer, fair value	45,724	7,370
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(4,603)	(243)
Debt Securities in an unrealized loss position, fair value	301,802	260,511
Debt Securities in an unrealized loss position, unrealized losses	$ (22,699)	$ (3,158)
Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	120	46
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 115,320	$ 92,217
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(7,950)	(1,648)
Debt Securities in an unrealized loss position 12 months or longer, fair value	2,495
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(248)
Debt Securities in an unrealized loss position, fair value	117,815	92,217
Debt Securities in an unrealized loss position, unrealized losses	$ (8,198)	$ (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	$ 3,479
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(133)
Debt Securities in an unrealized loss position 12 months or longer, fair value	76	$ 75
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(8)	(8)
Debt Securities in an unrealized loss position, fair value	3,555	75
Debt Securities in an unrealized loss position, unrealized losses	$ (141)	$ (8)