Note 4 - Securities - Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Amortized cost, due in one year or less, available for sale securities	$ 47,263
Fair value, due in one year or less, available for sale securities	46,985
Amortized cost, due after one year through five years, available for sale securities	181,571
Fair value, due after one year through five years, available for sale securities	176,935
Amortized cost, due after five years through ten years, available for sale securties	78,203
Fair value, due after five years through ten years, available for sale securities	75,727
Amortized cost, due after ten years, available for sale securities	38,223
Fair value, due after ten years, available for sale securities	37,564
Amortized cost, total securities available for sale	345,260	$ 336,075
Fair value, total securities available for sale	337,211	331,387
Amortized cost, due in one year or less, held to maturity securities	12,536
Fair value, due in one year or less, held to maturity securities	12,714
Amortized cost, due after one year through five years, held to maturity securities	21,962
Fair value, due after one year through five years, held to maturity securities	22,712
Amortized cost, due after five years through ten years, held to maturity securities	27,323
Fair value, due after give years through ten years, held to maturity securities	27,869
Amortized cost, due after ten years, held to maturity securities	61,084
Fair value, due after ten years, held to maturity securities	61,254
Amortized cost, total securities held to maturity	122,905	127,164
Fair value, total securities held to maturity	$ 124,549	$ 130,113