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Note 11 - Restrictions on Dividends (Details Textual) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Cash Dividends Paid to Parent Company by Consolidated Subsidiaries | $ 8,141 | $ 9,071 | $ 7,930
Payments of Dividends | $ 8,141 | 8,071 | $ 7,930
Period of Restriction on Retained Net Income Without Prior Approval | 2 years |  |
Statutory Accounting Practices, Statutory Amount Available for Dividend Payments without Regulatory Approval | $ 20,820 |  |
National Bankshares Financial Services [Member] |  |  |
Payments of Dividends |  | $ 350 |

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- Definition Period of restrictions on banking or savings institution's ability to pay dividends. + References No definition available. + Details
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- Definition This element represents disclosure of the aggregate cash dividends paid to the entity by consolidated subsidiaries. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-04.(b)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24072-122690 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 235 -Section S99 -Paragraph 2 -Subparagraph (SX 210.9-06) -URI http://asc.fasb.org/extlink&oid=6882215&loc=d3e537971-122884 + Details
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- Definition Cash outflow in the form of capital distributions and dividends to common shareholders, preferred shareholders and noncontrolling interests. + 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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- Definition Amount of dividends that can be declared or paid without approval of regulatory agency. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08.(e)) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690 + Details
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