Note 3 - Securities - Securities Available-for-sale (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Securities available-for-sale, amortized costs	$ 431,428	$ 336,075
Securities available-for-sale, gross unrealized gains	1,709	954
Securities available-for-sale, gross unrealized losses	8,127	5,642
Securities available-for-sale, fair values	425,010	331,387
US Government Agencies Debt Securities [Member]
Securities available-for-sale, amortized costs	306,264	312,604
Securities available-for-sale, gross unrealized gains	449	609
Securities available-for-sale, gross unrealized losses	6,666	5,494
Securities available-for-sale, fair values	300,047	307,719
US States and Political Subdivisions Debt Securities [Member]
Securities available-for-sale, amortized costs	118,564	16,853
Securities available-for-sale, gross unrealized gains	1,218	100
Securities available-for-sale, gross unrealized losses	1,166	119
Securities available-for-sale, fair values	118,616	16,834
Collateralized Mortgage Backed Securities [Member]
Securities available-for-sale, amortized costs	586	602
Securities available-for-sale, gross unrealized gains	42	57
Securities available-for-sale, gross unrealized losses	0	0
Securities available-for-sale, fair values	628	659
Corporate Debt Securities [Member]
Securities available-for-sale, amortized costs	6,014	6,016
Securities available-for-sale, gross unrealized gains		188
Securities available-for-sale, gross unrealized losses	295	29
Securities available-for-sale, fair values	$ 5,719	$ 6,175