Note 4 - Debt Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	174	321
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 84,182	$ 34,651
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(287)	(296)
Debt Securities in an unrealized loss position 12 months or longer, fair value	101,044	254,299
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(990)	(9,126)
Debt Securities in an unrealized loss position, fair value	185,226	288,950
Debt Securities in an unrealized loss position, unrealized losses	$ (1,277)	$ (9,422)
US Government Agencies Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	36	51
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 28,857
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(141)
Debt Securities in an unrealized loss position 12 months or longer, fair value	20,427	$ 68,409
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(72)	(2,072)
Debt Securities in an unrealized loss position, fair value	49,284	68,409
Debt Securities in an unrealized loss position, unrealized losses	$ (213)	$ (2,072)
US States and Political Subdivisions Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	7	81
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 2,431	$ 21,657
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(14)	(204)
Debt Securities in an unrealized loss position 12 months or longer, fair value	515	10,558
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(5)	(260)
Debt Securities in an unrealized loss position, fair value	2,946	32,215
Debt Securities in an unrealized loss position, unrealized losses	$ (19)	$ (464)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	66	111
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 28,482	$ 12,561
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(50)	(91)
Debt Securities in an unrealized loss position 12 months or longer, fair value	52,398	108,802
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(454)	(4,160)
Debt Securities in an unrealized loss position, fair value	80,880	121,363
Debt Securities in an unrealized loss position, unrealized losses	$ (504)	$ (4,251)
Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	64	73
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 24,412	$ 433
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(82)	(1)
Debt Securities in an unrealized loss position 12 months or longer, fair value	27,625	62,467
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(453)	(2,548)
Debt Securities in an unrealized loss position, fair value	52,037	62,900
Debt Securities in an unrealized loss position, unrealized losses	$ (535)	$ (2,549)
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	79	116
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(6)	(6)
Debt Securities in an unrealized loss position, fair value	79	116
Debt Securities in an unrealized loss position, unrealized losses	$ (6)	$ (6)
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security		4
Debt Securities in an unrealized loss position 12 months or longer, fair value		$ 3,947
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses		(80)
Debt Securities in an unrealized loss position, fair value		3,947
Debt Securities in an unrealized loss position, unrealized losses		$ (80)