Note 3 - Securities - Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Due in one year or less, available for sale, amortized cost	$ 4,600
Due in one year or less, available for sale, fair value	4,597
Due in one year or less, held to maturity, amortized cost	1,206
Due in one year or less, held to maturity, fair value	1,213
Due in over one to five years, available for sale, amortized cost	10,931
Due in over one to five years, available for sale, fair value	10,706
Due in over one to five years, held to maturity, amortized cost	6,748
Due in over one to five years, held to maturity, fair value	6,955
Due in over five to ten years, available for sale, amortized cost
Due in over five to ten years, available for sale, fair value
Due in over five to ten years, held to maturity, amortized cost	7,137
Due in over five to ten years, held to maturity, fair value	7,456
Due after ten years, available for sale, amortized cost
Due after ten years, available for sale, fair value
Due after ten years, held to maturity, amortized cost	2,259
Due after ten years, held to maturity, fair value	2,182
Agency mortgage-backed securities, residential, available for sale, amortized cost	92,822
Agency mortgage-backed securities, residential, available for sale, fair value	90,154
Agency mortgage-backed securities, residential, held to maturity, amortized cost	3
Agency mortgage-backed securities, residential, held to maturity, fair value	3
Total debt securities, available for sale, amortized cost	108,353	$ 102,455
Total debt securities, available for sale, fair value	105,457	101,125
Total debt securities, held to maturity, amortized cost	17,353	17,581
Securities held to maturity	$ 17,809	$ 18,079