Note 9 - Fair Value Accounting and Measurement - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Investment securities available for sale, at fair value	$ 369,111	$ 315,580
Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	369,111	315,580
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	369,111	315,580
Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
US States and Political Subdivisions Debt Securities [Member]
Investment securities available for sale, at fair value	97,143	39,282
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	97,143	39,282
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	97,143	39,282
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
Asset-backed Securities, Issued by US Government Agencies [Member]
Investment securities available for sale, at fair value	73,618	28,858
Asset-backed Securities, Issued by US Government Agencies [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	73,618	28,858
Asset-backed Securities, Issued by US Government Agencies [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
Asset-backed Securities, Issued by US Government Agencies [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	73,618	28,858
Asset-backed Securities, Issued by US Government Agencies [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
Asset-backed Securities, Issued by Private Enterprises [Member]
Investment securities available for sale, at fair value	32,747	40,855
Asset-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	32,747	40,855
Asset-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
Asset-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	32,747	40,855
Asset-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
Corporate Debt Securities [Member]
Investment securities available for sale, at fair value	33,230	9,643
Corporate Debt Securities [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	33,230	9,643
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	33,230	9,643
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
US Small Business Administration Securities [Member]
Investment securities available for sale, at fair value	23,864	28,459
US Small Business Administration Securities [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	23,864	28,459
US Small Business Administration Securities [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
US Small Business Administration Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	23,864	28,459
US Small Business Administration Securities [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment securities available for sale, at fair value	92,402	160,167
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	92,402	160,167
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	92,402	160,167
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Investment securities available for sale, at fair value	16,107	8,316
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	16,107	8,316
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	0	0
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	16,107	8,316
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Fair Value, Inputs, Level 3 [Member] | Fair Value, Recurring [Member]
Investment securities available for sale, at fair value	$ 0	$ 0