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Note 4 - Securities (Details Textual) $ in Thousands | Mar. 31, 2018 USD ($) | Dec. 31, 2017 USD ($)
--- | --- | ---
Number of Temporarily Impaired Securities | 377 |
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value | $ 341,058 |
Continuous Unrealized Loss Position Aggregate Losses | $ 9,260 |
Number of Temporarily Impaired Securities Greater than Twelve Months | 238 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | $ 230,059 | $ 229,675
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | 6,369 | 4,750
Federal Home Loan Bank of Atlanta [Member] | National Bank of Blacksburg [Member] |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged | 488,193 |
Restricted Stock [Member] |  |
Restricted Investments | $ 1,221 | 1,200
US Government Agencies Debt Securities [Member] |  |
Number of Temporarily Impaired Securities | 233 |
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value | $ 226,261 |
Continuous Unrealized Loss Position Aggregate Losses | 6,103 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | 226,261 | 225,738
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | $ 6,103 | 4,623
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 | $ 2,889 |
Continuous Unrealized Loss Position Aggregate Losses | 198 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | 2,889 | 2,989
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | $ 198 | 98
Corporate Debt Securities [Member] |  |
Number of Temporarily Impaired Securities | 1 |
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value | $ 909 |
Continuous Unrealized Loss Position Aggregate Losses | 68 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | 909 | 948
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | $ 68 | $ 29

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- Definition This item represents the aggregate fair value of investments in debt and equity securities categorized as held-to-maturity and available for sale securities that have been in a continuous unrealized loss position. + References No definition available. + Details
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- Definition Amount of the excess of amortized cost basis over fair value of securities that have been in a loss position for twelve months or longer for securities. + References No definition available. + Details
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- Definition Amount of the excess of amortized cost basis over fair value of securities that are in a loss position. + References No definition available. + Details
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- Definition This item represents the aggregate fair value of investments in debt and equity securities that have been in a continuous unrealized loss position for twelve months or longer. + References No definition available. + Details
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- Definition Amount of the collateral pledged in support of federal home loan bank advances outstanding. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 + Details
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