Note 7 - Fair Value Measurement - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available-for-sale securities	$ 53,594	$ 52,975	[1]
US Government Agencies Debt Securities [Member]
Available-for-sale securities	13,356	12,444
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities	13,356	12,444
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available-for-sale securities	21,193	19,768
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities	21,193	19,768
Corporate Debt Securities [Member]
Available-for-sale securities	6,558	5,066
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities	6,558	5,066
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	12,487	15,697
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Available-for-sale securities	$ 12,487	$ 15,697

[1] Derived from consolidated audited financial statements.