Note 6 - Debt Securities in a Continuous Unrealized Loss Position (Details) $ in Thousands	Sep. 30, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	182	321
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 74,508	$ 34,651
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(228)	(296)
Debt Securities in an unrealized loss position 12 months or longer, fair value	117,842	254,299
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(1,143)	(9,126)
Debt Securities in an unrealized loss position, fair value	192,350	288,950
Debt Securities in an unrealized loss position, unrealized losses	$ (1,371)	$ (9,422)
US Treasury Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	1
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	$ 23,450	$ 0
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(60)	0
Debt Securities in an unrealized loss position 12 months or longer, fair value	22,393	68,409
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(106)	(2,072)
Debt Securities in an unrealized loss position, fair value	45,843	68,409
Debt Securities in an unrealized loss position, unrealized losses	$ (166)	$ (2,072)
US States and Political Subdivisions Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	4	81
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 1,383	$ 21,657
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(11)	(204)
Debt Securities in an unrealized loss position 12 months or longer, fair value	516	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	1,899	32,215
Debt Securities in an unrealized loss position, unrealized losses	$ (16)	$ (464)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	80	111
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 34,962	$ 12,561
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(111)	(91)
Debt Securities in an unrealized loss position 12 months or longer, fair value	62,989	108,802
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(616)	(4,160)
Debt Securities in an unrealized loss position, fair value	97,951	121,363
Debt Securities in an unrealized loss position, unrealized losses	$ (727)	$ (4,251)
Collateralized Mortgage Obligations [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	57	73
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 12,709	$ 433
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(44)	(1)
Debt Securities in an unrealized loss position 12 months or longer, fair value	30,862	62,467
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(408)	(2,548)
Debt Securities in an unrealized loss position, fair value	43,571	62,900
Debt Securities in an unrealized loss position, unrealized losses	$ (452)	$ (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	78	116
Debt Securities in an unrealized loss position 12 months or longer, unrealized losses	(8)	(6)
Debt Securities in an unrealized loss position, fair value	78	116
Debt Securities in an unrealized loss position, unrealized losses	$ (8)	$ (6)
Corporate Debt Securities [Member]
Schedule Of Available For Sale Securities [Line Items]
No. of debt securities | security	3	4
Debt Securities in an unrealized loss position less than 12 months, fair value	$ 2,004
Debt Securities in an unrealized loss position less than 12 months, unrealized losses	(2)	$ 0
Debt Securities in an unrealized loss position 12 months or longer, fair value	1,004	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	3,008	3,947
Debt Securities in an unrealized loss position, unrealized losses	$ (2)	$ (80)