Note 5 - Securities - Securities in a Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Less than 12 months, fair value	$ 42,702	$ 147,169
Less than 12 months, gross unrealized losses	364	3,183
12 months or greater, fair value	87,854	15,248
12 months or greater, gross unrealized losses	2,144	645
Total, fair value	130,556	162,417
Total, gross unrealized losses	2,508	3,828
US Government Agencies Debt Securities [Member]
Less than 12 months, fair value	4,136	4,535
Less than 12 months, gross unrealized losses	56	50
12 months or greater, fair value	2,004
12 months or greater, gross unrealized losses	12
Total, fair value	6,140	4,535
Total, gross unrealized losses	68	50
Corporate Debt Securities [Member]
Less than 12 months, fair value	4,448	2,010
Less than 12 months, gross unrealized losses	69	31
12 months or greater, fair value	2,007	4,515
12 months or greater, gross unrealized losses	23	21
Total, fair value	6,455	6,525
Total, gross unrealized losses	92	52
Collateralized Mortgage Backed Securities [Member]
Less than 12 months, fair value	8,320	86,091
Less than 12 months, gross unrealized losses	71	1,974
12 months or greater, fair value	71,182	9,885
12 months or greater, gross unrealized losses	1,753	440
Total, fair value	79,502	95,976
Total, gross unrealized losses	1,824	2,414
US States and Political Subdivisions Debt Securities [Member]
Less than 12 months, fair value	25,798	54,533
Less than 12 months, gross unrealized losses	168	1,128
12 months or greater, fair value	11,927	207
12 months or greater, gross unrealized losses	259	5
Total, fair value	37,725	54,740
Total, gross unrealized losses	427	1,133
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	734	641
12 months or greater, gross unrealized losses	97	179
Total, fair value	734	641
Total, gross unrealized losses	$ 97	$ 179