Note 8 - Securities Sold Under Agreements to Repurchase - Federal Funds Purchased and Other Short-term Borrowings (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Securities sold under agreements to repurchase	$ 34,252	$ 36,370
Average balance during the year	35,063	107,179
Maximum month-end balance during the year	$ 38,079	$ 140,218
Average interest rate during the year	0.22%	2.74%
Average interest rate at year-end	0.22%	0.36%