Note 5 - Fair Value Measurements - Assets Measured on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investment securities available for sale, at fair value	$ 91,262	$ 95,283
US Government Agencies Debt Securities [Member]
Investment securities available for sale, at fair value	8,305	8,719
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities available for sale, at fair value	17,378	18,510
Debt Securities [Member]
Investment securities available for sale, at fair value		94,658
Equity Securities [Member]
Investment securities available for sale, at fair value		625
Fair Value, Measurements, Recurring [Member]
Investment securities available for sale, at fair value	91,905	95,283
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member]
Investment securities available for sale, at fair value	8,305	8,719
Fair Value, Measurements, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, at fair value	65,579	67,429
Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities available for sale, at fair value	17,378	18,510
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member]
Investment securities available for sale, at fair value	91,262	94,658
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Investment securities available for sale, at fair value	643	625
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Investment securities available for sale, at fair value	393
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member]
Investment securities available for sale, at fair value
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, at fair value
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities available for sale, at fair value
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member]
Investment securities available for sale, at fair value
Fair Value, Inputs, Level 1 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Investment securities available for sale, at fair value	393
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Investment securities available for sale, at fair value	91,512	95,283
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member]
Investment securities available for sale, at fair value	8,305	8,719
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, at fair value	65,579	67,429
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities available for sale, at fair value	17,378	18,510
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member]
Investment securities available for sale, at fair value	91,262	94,658
Fair Value, Inputs, Level 2 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Investment securities available for sale, at fair value	250	625
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Investment securities available for sale, at fair value
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member]
Investment securities available for sale, at fair value
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, at fair value
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities available for sale, at fair value
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Debt Securities [Member]
Investment securities available for sale, at fair value
Fair Value, Inputs, Level 3 [Member] | Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Investment securities available for sale, at fair value