Note 6 - Loans and the Allowance for Loan Losses - Impaired Loans (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Recorded investment, with an allowance recorded	$ 1,436	$ 1,539
Unpaid principal balance, with an allowance recorded	1,543	1,583
Related allowance	536	887
Average recorded investment, with an allowance recorded	1,830	2,322
Recorded investment, with no allowance recorded	12,013	10,470
Unpaid principal balance, with no allowance recorded	14,459	12,145
Average recorded investment, with no allowance recorded	11,775	10,873
Recorded investment	13,449	12,009
Unpaid principal balance	16,002	13,728
Average recorded investment	13,605	13,195
Commercial Real Estate Portfolio Segment [Member] \| Construction and Land [Member]
Recorded investment, with an allowance recorded	90	0
Unpaid principal balance, with an allowance recorded	90	0
Related allowance	36	0
Average recorded investment, with an allowance recorded	74	655
Recorded investment, with no allowance recorded	3	143
Unpaid principal balance, with no allowance recorded	9	152
Average recorded investment, with no allowance recorded	44	124
Recorded investment	93	143
Unpaid principal balance	99	152
Average recorded investment	118	779
Commercial Real Estate Portfolio Segment [Member] \| Farmland [Member]
Recorded investment, with an allowance recorded	0	0
Unpaid principal balance, with an allowance recorded	0	0
Related allowance	0	0
Average recorded investment, with an allowance recorded	0	0
Recorded investment, with no allowance recorded	0	0
Unpaid principal balance, with no allowance recorded	0	0
Average recorded investment, with no allowance recorded	0	0
Recorded investment	0	0
Unpaid principal balance	0	0
Average recorded investment	0	0
Commercial Real Estate Portfolio Segment [Member] \| Nonfarm Nonresidential [Member]
Recorded investment, with an allowance recorded	316	368
Unpaid principal balance, with an allowance recorded	341	368
Related allowance	46	98
Average recorded investment, with an allowance recorded	462	31
Recorded investment, with no allowance recorded	5,515	705
Unpaid principal balance, with no allowance recorded	5,653	729
Average recorded investment, with no allowance recorded	3,402	3,730
Recorded investment	5,831	1,073
Unpaid principal balance	5,994	1,097
Average recorded investment	3,864	3,761
Residential Portfolio Segment [Member] \| Real Estate Residential One- to Four-Family [Member]
Recorded investment, with an allowance recorded	491	440
Unpaid principal balance, with an allowance recorded	540	470
Related allowance	125	252
Average recorded investment, with an allowance recorded	787	372
Recorded investment, with no allowance recorded	2,325	2,823
Unpaid principal balance, with no allowance recorded	2,744	3,276
Average recorded investment, with no allowance recorded	2,188	3,296
Recorded investment	2,816	3,263
Unpaid principal balance	3,284	3,746
Average recorded investment	2,975	3,668
Residential Portfolio Segment [Member] \| Multi-family Residential [Member]
Recorded investment, with an allowance recorded	0	0
Unpaid principal balance, with an allowance recorded	0	0
Related allowance	0	0
Average recorded investment, with an allowance recorded	0	0
Recorded investment, with no allowance recorded	0	0
Unpaid principal balance, with no allowance recorded	0	0
Average recorded investment, with no allowance recorded	0	0
Recorded investment	0	0
Unpaid principal balance	0	0
Average recorded investment	0	0
Commercial Portfolio Segment [Member]
Recorded investment, with an allowance recorded	539	695
Unpaid principal balance, with an allowance recorded	572	709
Related allowance	329	501
Average recorded investment, with an allowance recorded	502	1,252
Recorded investment, with no allowance recorded	3,729	6,637
Unpaid principal balance, with no allowance recorded	5,581	7,826
Average recorded investment, with no allowance recorded	5,898	3,680
Recorded investment	4,268	7,332
Unpaid principal balance	6,153	8,535
Average recorded investment	6,400	4,932
Consumer Portfolio Segment [Member]
Recorded investment, with an allowance recorded	0	36
Unpaid principal balance, with an allowance recorded	0	36
Related allowance	0	36
Average recorded investment, with an allowance recorded	5	12
Recorded investment, with no allowance recorded	441	162
Unpaid principal balance, with no allowance recorded	472	162
Average recorded investment, with no allowance recorded	243	43
Recorded investment	441	198
Unpaid principal balance	472	198
Average recorded investment	$ 248	$ 55

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953550-111524

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5258-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=d3e5212-111524

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