Note 10 - Fair Value Measurement - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale	$ 173,227	$ 171,507
Fair Value, Recurring [Member]
Assets	173,227	171,507
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets	173,227	171,507
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale	132,088	132,678
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Recurring [Member]
Debt Securities, Available-for-sale	132,088	132,678
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale	132,088	132,678
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale	41,139	38,829
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Recurring [Member]
Debt Securities, Available-for-sale	41,139	38,829
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Debt Securities, Available-for-sale	$ 41,139	$ 38,829