Note 13 - Stock Option Plan (Details) - Intrinsic Value Related to Stock Options Exercised - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tax Benefits and Intrinsic Value Related to Stock Options Exercised [Abstract]
Intrinsic value of stock options exercised	$ 204	$ 234	$ 148

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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Period Type:	duration