Note 3 - Securities - Securities by Contractual Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Amortized cost, due in one year or less, available for sale securities	$ 33,405
Fair value, due in one year or less, available for sale securities	33,238
Amortized cost, due after one year through five years, available for sale securities	192,388
Fair value, due after one year through five years, available for sale securities	189,005
Amortized cost, due after five years through ten years, available for sale securties	72,001
Fair value, due after five years through ten years, available for sale securities	70,509
Amortized cost, due after ten years, available for sale securities	38,281
Fair value, due after ten years, available for sale securities	38,635
Amortized cost, total securities available for sale	336,075
Fair value, total securities available for sale	331,387	$ 304,282
Amortized cost, due in one year or less, held to maturity securities	11,906
Fair value, due in one year or less, held to maturity securities	12,088
Amortized cost, due after one year through five years, held to maturity securities	24,403
Fair value, due after one year through five years, held to maturity securities	25,359
Amortized cost, due after five years through ten years, held to maturity securities	25,242
Fair value, due after give years through ten years, held to maturity securities	25,892
Amortized cost, due after ten years, held to maturity securities	65,613
Fair value, due after ten years, held to maturity securities	66,774
Amortized cost, total securities held to maturity	127,164	134,957
Fair value, total securities held to maturity	$ 130,113	$ 137,692