Note 4 - Securities - Securities Held-to-maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Securities held-to-maturity, amortized costs	$ 129,750	$ 134,957
Securities held-to-maturity, gross unrealized gains	4,177	3,817
Securities held-to-maturity, gross unrealized losses	68	1,082
Securities held-to-maturity, fair values	133,859	137,692
US Government Agencies Debt Securities [Member]
Securities held-to-maturity, amortized costs	3,934	3,934
Securities held-to-maturity, gross unrealized gains	215	201
Securities held-to-maturity, gross unrealized losses	0	0
Securities held-to-maturity, fair values	4,149	4,135
US States and Political Subdivisions Debt Securities [Member]
Securities held-to-maturity, amortized costs	124,611	129,783
Securities held-to-maturity, gross unrealized gains	3,923	3,579
Securities held-to-maturity, gross unrealized losses	68	1,082
Securities held-to-maturity, fair values	128,466	132,280
Collateralized Mortgage Backed Securities [Member]
Securities held-to-maturity, amortized costs	225	265
Securities held-to-maturity, gross unrealized gains	24	30
Securities held-to-maturity, gross unrealized losses	0	0
Securities held-to-maturity, fair values	249	295
Corporate Debt Securities [Member]
Securities held-to-maturity, amortized costs	980	975
Securities held-to-maturity, gross unrealized gains	15	7
Securities held-to-maturity, gross unrealized losses	0	0
Securities held-to-maturity, fair values	$ 995	$ 982