Note 10 - Financial Instrument Commitments (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Commitments And Contingencies Disclosure [Line Items]
Commitments to extend credit and unused lines of credit	$ 308,255	$ 328,752
Commitments to Extend Credit [Member]
Commitments And Contingencies Disclosure [Line Items]
Commitments to extend credit and unused lines of credit	289,971	313,541
Standby Letters of Credit [Member]
Commitments And Contingencies Disclosure [Line Items]
Commitments to extend credit and unused lines of credit	$ 18,284	$ 15,211

Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109250915&loc=d3e13537-108611

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration