Note 7 - Fair Value Measurement - Fair Value of Financial Assets and Liabilities Measured on Recurring Basis (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016
Available-for-sale securities	$ 48,665	$ 52,975	[1]
US Government Agencies Debt Securities [Member]
Available-for-sale securities	11,245	12,444
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities	11,245	12,444
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Available-for-sale securities	19,744	19,768
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities	19,744	19,768
Corporate Debt Securities [Member]
Available-for-sale securities	4,605	5,066
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities	4,605	5,066
US States and Political Subdivisions Debt Securities [Member]
Available-for-sale securities	13,071	15,697
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Available-for-sale securities	$ 13,071	$ 15,697

[1] Derived from consolidated audited financial statements.