Note 3 - Loans and Allowance for Loan Losses - Impaired Loans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation allowance	$ 1,249,000	$ 602,000
Loans recorded balance	10,827,000	8,699,000
Loans unpaid principal	12,060,000	10,384,000
Loans average investment in impaired loans	9,331,000	12,010,000	$ 8,110,000
Loans interest income recognized	6,000	2,000	$ 4,000
Residential Portfolio Segment [Member] | Real Estate Residential, One To Four Family Units [Member]
Loans without a specific valuation allowance, recorded balance	3,180,000	2,006,000
Loans without a specific valuation allowance, unpaid principal	3,180,000	2,006,000
Loans without a specific valuation allowance, average investment in impaired loans	2,170,000	2,165,000
Loans without a specific valuation allowance, interest income recognized	0	0
Loans with a specific valuation allowance, recorded balance	1,244,000	54,000
Loans with a specific valuation allowance, unpaid principal	1,244,000	54,000
Valuation allowance	127,000	14,000
Loans with a specific valuation allowance, average investment in impaired loans	247,000	27,000
Loans with a specific valuation allowance, interest income recognized	0	0
Loans recorded balance	4,424,000	2,060,000
Loans unpaid principal	4,424,000	2,060,000
Loans average investment in impaired loans	2,417,000	2,192,000
Loans interest income recognized	0	0
Residential Portfolio Segment [Member] | Real Estate Residential, Multi Family Units [Member]
Loans without a specific valuation allowance, recorded balance	775,000
Loans without a specific valuation allowance, unpaid principal	775,000
Loans without a specific valuation allowance, average investment in impaired loans	130,000
Loans without a specific valuation allowance, interest income recognized	5,000
Loans with a specific valuation allowance, recorded balance	0	0
Loans with a specific valuation allowance, unpaid principal	0	0
Valuation allowance	0	0
Loans with a specific valuation allowance, average investment in impaired loans	0	0
Loans with a specific valuation allowance, interest income recognized	0	0
Loans recorded balance	775,000
Loans unpaid principal	775,000
Loans average investment in impaired loans	130,000
Loans interest income recognized	5,000
Real Estate, Construction [Member]
Loans without a specific valuation allowance, recorded balance	2,840,000	3,017,000
Loans without a specific valuation allowance, unpaid principal	2,840,000	3,017,000
Loans without a specific valuation allowance, average investment in impaired loans	2,940,000	5,427,000
Loans without a specific valuation allowance, interest income recognized	0	0
Loans with a specific valuation allowance, recorded balance	1,612,000	2,430,000
Loans with a specific valuation allowance, unpaid principal	2,845,000	3,663,000
Valuation allowance	738,000	302,000
Loans with a specific valuation allowance, average investment in impaired loans	2,326,000	2,195,000
Loans with a specific valuation allowance, interest income recognized	0	0
Loans recorded balance	4,452,000	5,447,000
Loans unpaid principal	5,685,000	6,680,000
Loans average investment in impaired loans	5,266,000	7,622,000
Loans interest income recognized	0	0
Commercial Real Estate Portfolio Segment [Member]
Loans without a specific valuation allowance, recorded balance	161,000	161,000
Loans without a specific valuation allowance, unpaid principal	161,000	161,000
Loans without a specific valuation allowance, average investment in impaired loans	311,000	540,000
Loans without a specific valuation allowance, interest income recognized	0	0
Loans with a specific valuation allowance, recorded balance	0	0
Loans with a specific valuation allowance, unpaid principal	0	0
Valuation allowance	0	0
Loans with a specific valuation allowance, average investment in impaired loans		139,000
Loans with a specific valuation allowance, interest income recognized	0	0
Loans recorded balance	161,000	161,000
Loans unpaid principal	161,000	161,000
Loans average investment in impaired loans	311,000	679,000
Loans interest income recognized	0	0
Commercial Portfolio Segment [Member]
Loans without a specific valuation allowance, recorded balance	465,000	622,000
Loans without a specific valuation allowance, unpaid principal	465,000	622,000
Loans without a specific valuation allowance, average investment in impaired loans	536,000	868,000
Loans without a specific valuation allowance, interest income recognized	0	0
Loans with a specific valuation allowance, recorded balance	274,000	303,000
Loans with a specific valuation allowance, unpaid principal	274,000	755,000
Valuation allowance	246,000	241,000
Loans with a specific valuation allowance, average investment in impaired loans	456,000	447,000
Loans with a specific valuation allowance, interest income recognized	0	0
Loans recorded balance	739,000	925,000
Loans unpaid principal	739,000	1,377,000
Loans average investment in impaired loans	992,000	1,315,000
Loans interest income recognized	0	0
Consumer and Other Loans [Member]
Loans without a specific valuation allowance, recorded balance	3,000	3,000
Loans without a specific valuation allowance, unpaid principal	3,000	3,000
Loans without a specific valuation allowance, average investment in impaired loans	7,000	90,000
Loans without a specific valuation allowance, interest income recognized	1,000	2,000
Loans with a specific valuation allowance, recorded balance	273,000	103,000
Loans with a specific valuation allowance, unpaid principal	273,000	103,000
Valuation allowance	138,000	45,000
Loans with a specific valuation allowance, average investment in impaired loans	208,000	112,000
Loans with a specific valuation allowance, interest income recognized	0	0
Loans recorded balance	276,000	106,000
Loans unpaid principal	276,000	106,000
Loans average investment in impaired loans	215,000	202,000
Loans interest income recognized	$ 1,000	$ 2,000