Note 3 - Loans Receivable - Classifications of Loans Receivable (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Loans	$ 455,590	$ 444,195
Less allowance for loan losses	(3,860)	(3,758)	$ (3,636)
Loans, net	451,730	440,437
Construction Loan Portfolio Segment [Member] \| Residential [Member]
Loans	19,452	15,221
Less allowance for loan losses	(120)	(94)	(63)
Construction Loan Portfolio Segment [Member] \| Land Acquisition Development And Commercial [Member]
Loans	38,348	35,601
Less allowance for loan losses	(300)	(311)	(173)
Real Estate Portfolio Segment [Member] \| Residential [Member]
Loans	129,505	121,649
Less allowance for loan losses	(1,014)	(955)	(866)
Real Estate Portfolio Segment [Member] \| Commercial [Member]
Loans	173,803	173,999
Less allowance for loan losses	(1,528)	(1,603)	(1,516)
Commercial Industrial And Agricultural Portfolio Segment Excluding Overdrafts [Member]
Loans	58,276	61,129
Equity Lines Portfolio Segment [Member]
Loans	28,973	28,835
Less allowance for loan losses	(218)	(237)	(338)
Consumer Portfolio Segment [Member]
Loans	7,182	7,693
Less allowance for loan losses	(108)	(108)	$ (97)
Overdrafts Portfolio Segment [Member]
Loans	$ 51	$ 68

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

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