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Note 16 - Fair Value Measurements - Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Securities available for sale	$ 331,387	$ 304,282
Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0	0
Fair Value, Inputs, Level 2 [Member]
Securities available for sale	331,387	304,282
Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0	0
US Government Agencies Debt Securities [Member]
Securities available for sale	307,719	285,598
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0	0
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	307,719	285,598
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0	0
US States and Political Subdivisions Debt Securities [Member]
Securities available for sale	16,834	11,693
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0	0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	16,834	11,693
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0	0
Collateralized Mortgage Backed Securities [Member]
Securities available for sale	659	930
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0	0
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	659	930
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	0	0
Corporate Debt Securities [Member]
Securities available for sale	6,175	5,898
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale	0	0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale	6,175	5,898
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale	$ 0	0
Other Securities [Member]
Securities available for sale		163
Other Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Securities available for sale		0
Other Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Securities available for sale		163
Other Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Securities available for sale		$ 0

X

- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562

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