Note 2 - Investment Securities - Schedule of Investment Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Available for sale securities, amortized cost	$ 343,971	$ 331,267
Available for sale securities, gross unrealized gains	413	94
Available for sale securities, gross unrealized losses	(6,135)	(7,703)
Available for sale securities, fair value	338,249	323,658
US Government Agencies Debt Securities [Member]
Available for sale securities, amortized cost	336,376	326,694
Available for sale securities, gross unrealized gains	368	76
Available for sale securities, gross unrealized losses	(6,086)	(7,673)
Available for sale securities, fair value	330,658	319,097
US States and Political Subdivisions Debt Securities [Member]
Available for sale securities, amortized cost	4,527	4,573
Available for sale securities, gross unrealized gains	37	18
Available for sale securities, gross unrealized losses	(25)	(30)
Available for sale securities, fair value	4,539	$ 4,561
Corporate Debt Securities [Member]
Available for sale securities, amortized cost	2,052
Available for sale securities, gross unrealized gains	8
Available for sale securities, gross unrealized losses
Available for sale securities, fair value	2,060
Asset-backed Securities [Member]
Available for sale securities, amortized cost	1,016
Available for sale securities, gross unrealized gains
Available for sale securities, gross unrealized losses	(24)
Available for sale securities, fair value	$ 992

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

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)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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-Publisher FASB
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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
-Paragraph 1
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