Note 6 - Troubled Debt Restructurings - Performing TDR Loans (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Performing TDR loans	$ 1,900,000	$ 2,400,000
Percentage of total loans held for investment, net	0.40%	0.50%
Performing Financial Instruments [Member]
Performing TDR loans	$ 556,000	$ 877,000	$ 1,422,000	$ 5,207,000	$ 8,366,000
Percentage of total loans held for investment, net	0.10%	0.10%	0.30%	1.10%	1.70%
Performing Financial Instruments [Member] | Residential Portfolio Segment [Member]
Performing TDR loans	$ 0	$ 0	$ 0
Performing Financial Instruments [Member] | Residential Portfolio Segment [Member] | Real Estate Loan [Member]
Performing TDR loans	0	0	0	$ 287,000	$ 0
Performing Financial Instruments [Member] | Commercial Portfolio Segment [Member]
Performing TDR loans	461,000	770,000	1,141,000
Performing Financial Instruments [Member] | Commercial Portfolio Segment [Member] | Real Estate Loan [Member]
Performing TDR loans	461,000	765,000	1,132,000	1,887,000	5,901,000
Performing Financial Instruments [Member] | Commercial Portfolio Segment [Member] | Commercial Construction [Member]
Performing TDR loans	0	0	0	2,762,000	29,000
Performing Financial Instruments [Member] | Commercial Portfolio Segment [Member] | Lots and Raw Land [Member]
Performing TDR loans	0	0	0	0	1,667,000
Performing Financial Instruments [Member] | Commercial Portfolio Segment [Member] | Commercial and Industrial [Member]
Performing TDR loans	0	5,000	9,000	13,000	16,000
Performing Financial Instruments [Member] | Consumer Portfolio Segment [Member]
Performing TDR loans	95,000	107,000	281,000
Performing Financial Instruments [Member] | Consumer Portfolio Segment [Member] | Real Estate Loan [Member]
Performing TDR loans	0	0	165,000	171,000	60,000
Performing Financial Instruments [Member] | Consumer Portfolio Segment [Member] | Lots and Raw Land [Member]
Performing TDR loans	95,000	107,000	60,000	69,000	667,000
Performing Financial Instruments [Member] | Consumer Portfolio Segment [Member] | Home Equity Loan [Member]
Performing TDR loans	0	0	0	0	0
Performing Financial Instruments [Member] | Consumer Portfolio Segment [Member] | Other Loans [Member]
Performing TDR loans	$ 0	$ 0	$ 56,000	$ 18,000	$ 26,000