Note 9 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Investment securities	$ 112,329	$ 101,595
Fair Value, Inputs, Level 2 [Member]
Investment securities	112,329	101,595
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities	80,416	74,911
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Inputs, Level 2 [Member]
Investment securities	80,416	74,911
US States and Political Subdivisions Debt Securities [Member]
Investment securities	31,913	26,684
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Investment securities	$ 31,913	$ 26,684