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Note 3 - Securities (Details Textual) $ in Thousands | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Number of Temporarily Impaired Securities | 343 |
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value | $ 316,743 |
Continuous Unrealized Loss Position Aggregate Losses | $ 5,815 |
Number of Temporarily Impaired Securities Greater than Twelve Months | 236 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | $ 229,675 | $ 2,475
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | 4,750 | 178
Available-for-sale Securities Pledged as Collateral | 194,980 | 178,121
Federal Home Loan Bank of Atlanta [Member] | National Bank of Blacksburg [Member] |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Available to be Pledged | 494,666 |
Restricted Stock [Member] |  |
Restricted Investments | $ 1,200 | 1,170
US Government Agencies Debt Securities [Member] |  |
Number of Temporarily Impaired Securities | 231 |
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value | $ 225,738 |
Continuous Unrealized Loss Position Aggregate Losses | 4,623 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | 225,738 | 996
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | $ 4,623 | 4
US States and Political Subdivisions Debt Securities [Member] |  |
Number of Temporarily Impaired Securities | 4 |
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value | $ 2,989 |
Continuous Unrealized Loss Position Aggregate Losses | 98 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | 2,989 | 1,316
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | $ 98 | 148
Corporate Debt Securities [Member] |  |
Number of Temporarily Impaired Securities | 1 |
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value | $ 948 |
Continuous Unrealized Loss Position Aggregate Losses | 29 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | 948 | 0
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | 29 | 0
Other Securities [Member] |  |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value |  | 163
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses |  | $ 26
Available-for-sale Securities, Gross Realized Gains | 4 |
Available-for-sale Securities Sold, Book Value | $ 189 |

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- Definition This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 + Details
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