Note 5 - Securities - Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Less than 12 months, fair value	$ 134,306	$ 42,702
Less than 12 months, gross unrealized losses	3,184	364
12 months or greater, fair value	81,489	87,854
12 months or greater, gross unrealized losses	3,765	2,144
Total, fair value	215,795	130,556
Total, gross unrealized losses	6,949	2,508
US Government Agencies Debt Securities [Member]
Less than 12 months, fair value	9,515	4,136
Less than 12 months, gross unrealized losses	253	56
12 months or greater, fair value	1,837	2,004
12 months or greater, gross unrealized losses	70	12
Total, fair value	11,352	6,140
Total, gross unrealized losses	323	68
Corporate Debt Securities [Member]
Less than 12 months, fair value	2,020	4,448
Less than 12 months, gross unrealized losses	2	69
12 months or greater, fair value	2,273	2,007
12 months or greater, gross unrealized losses	228	23
Total, fair value	4,293	6,455
Total, gross unrealized losses	230	92
Collateralized Mortgage Backed Securities [Member]
Less than 12 months, fair value	66,459	8,320
Less than 12 months, gross unrealized losses	1,968	71
12 months or greater, fair value	63,492	71,182
12 months or greater, gross unrealized losses	2,951	1,753
Total, fair value	129,951	79,502
Total, gross unrealized losses	4,919	1,824
US States and Political Subdivisions Debt Securities [Member]
Less than 12 months, fair value	56,312	25,798
Less than 12 months, gross unrealized losses	961	168
12 months or greater, fair value	13,167	11,927
12 months or greater, gross unrealized losses	445	259
Total, fair value	69,479	37,725
Total, gross unrealized losses	1,406	427
Other Debt Obligations [Member]
Less than 12 months, fair value	0	0
Less than 12 months, gross unrealized losses	0	0
12 months or greater, fair value	720	734
12 months or greater, gross unrealized losses	71	97
Total, fair value	720	734
Total, gross unrealized losses	$ 71	$ 97