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Note 9 - Dividends (Details Textual) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Payments of Ordinary Dividends, Common Stock |  |  |  |  | $ 4,361 | $ 3,252 | $ 3,342
Paid Quarterly [Member] |  |  |  |  |  |  |
Common Stock, Dividends, Per Share, Declared | $ 0.025 | $ 0.025 | $ 0.015 | $ 0.015 |  |  |

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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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- Definition Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 15 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585 + Details
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