Note 6 - Debt Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2020 USD ($) security	Dec. 31, 2019 USD ($) security
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	57	174
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 87,479	$ 84,182
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(438)	(287)
Debt Securities in an unrealized loss position 12 months or longer, fair value	68	101,044
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(16)	(990)
Debt Securities in an unrealized loss position, fair value	87,547	185,226
Debt Securities in an unrealized loss position, unrealized losses	$ (454)	$ (1,277)
US Government Agencies Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	17	36
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 32,451	$ 28,857
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(152)	(141)
Debt Securities in an unrealized loss position 12 months or longer, fair value		20,427
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses		(72)
Debt Securities in an unrealized loss position, fair value	32,451	49,284
Debt Securities in an unrealized loss position, unrealized losses	$ (152)	$ (213)
US States and Political Subdivisions Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	24	7
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 13,828	$ 2,431
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(140)	(14)
Debt Securities in an unrealized loss position 12 months or longer, fair value		515
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses		(5)
Debt Securities in an unrealized loss position, fair value	13,828	2,946
Debt Securities in an unrealized loss position, unrealized losses	$ (140)	$ (19)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	10	66
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 32,864	$ 28,482
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(112)	(50)
Debt Securities in an unrealized loss position 12 months or longer, fair value		52,398
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses		(454)
Debt Securities in an unrealized loss position, fair value	32,864	80,880
Debt Securities in an unrealized loss position, unrealized losses	$ (112)	$ (504)
Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	4	64
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 5,361	$ 24,412
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(9)	(82)
Debt Securities in an unrealized loss position 12 months or longer, fair value		27,625
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses		(453)
Debt Securities in an unrealized loss position, fair value	5,361	52,037
Debt Securities in an unrealized loss position, unrealized losses	$ (9)	$ (535)
Collateralized Debt Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	1	1
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 0	$ 0
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	0	0
Debt Securities in an unrealized loss position 12 months or longer, fair value	68	79
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(16)	(6)
Debt Securities in an unrealized loss position, fair value	68	79
Debt Securities in an unrealized loss position, unrealized losses	$ (16)	(6)
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	1
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 2,975
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(25)	$ 0
Debt Securities in an unrealized loss position, fair value	2,975
Debt Securities in an unrealized loss position, unrealized losses	$ (25)