Note 4 - Securities - Sales of Securities (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Proceeds from sales of securities	$ 64,349	$ 51,025	$ 71,277
Gross realized gains on sales of securities	315	352	556
Gross realized losses on sales of securities	(178)	(108)	(113)
Gain on investment securities, net	137	244	443
US Government Agencies Debt Securities [Member]
Proceeds from sales of securities	64,349	51,025	71,277
Gross realized gains on sales of securities		25	16
Gross realized losses on sales of securities		(13)	(33)
US States and Political Subdivisions Debt Securities [Member]
Gross realized gains on sales of securities	161	188	97
Gross realized losses on sales of securities	(102)	(3)	(29)
Residential Mortgage Backed Securities and Collateralized Mortgage Obligations [Member]
Gross realized gains on sales of securities	52	17	142
Gross realized losses on sales of securities	(56)	(64)	(12)
Corporate Debt Securities [Member]
Gross realized gains on sales of securities	79	105	161
Gross realized losses on sales of securities	(3)	(27)	(14)
Commercial Mortgage Backed Securities [Member]
Gross realized gains on sales of securities	3	4	14
Gross realized losses on sales of securities	(17)	(1)
Asset-backed Securities [Member]
Gross realized gains on sales of securities	20	13	126
Gross realized losses on sales of securities			$ (25)

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563

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- Definition

This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

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This item represents the gross loss realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities.

+ References

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- Definition

The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

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