XML 46 R35.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Note 4 - Securities (Details Textual) $ in Thousands | Mar. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
--- | --- | ---
Number of Temporarily Impaired Securities | 314 |
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value | $ 292,607 |
Continuous Unrealized Loss Position Aggregate Losses | $ 5,343 |
Number of Temporarily Impaired Securities Greater than Twelve Months | 5 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | $ 3,564 | $ 2,475
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | 88 | 178
Federal Home Loan Bank of Atlanta [Member] | National Bank of Blacksburg [Member] |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged | 478,903 |
Restricted Stock [Member] |  |
Restricted Investments | $ 1,200 | 1,170
US Government Agencies Debt Securities [Member] |  |
Number of Temporarily Impaired Securities | 2 |
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value | $ 1,995 |
Continuous Unrealized Loss Position Aggregate Losses | 4 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | 1,995 | 996
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | $ 4 | 4
US States and Political Subdivisions Debt Securities [Member] |  |
Number of Temporarily Impaired Securities | 2 |
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value | $ 1,389 |
Continuous Unrealized Loss Position Aggregate Losses | 75 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | 1,389 | 1,316
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | $ 75 | 148
Other Securities [Member] |  |
Number of Temporarily Impaired Securities | 1 |
Available-for-sale and Held to Maturity Securities Continuous Unrealized Loss Position Fair Value | $ 180 |
Continuous Unrealized Loss Position Aggregate Losses | 9 |
Continuous Unrealized Loss Position Twelve Months or Longer Fair Value | 180 | 163
Continuous Unrealized Loss Position 12 Months or Longer Aggregate Losses | $ 9 | $ 26

X
- 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
Name: | nksh_AvailableforsaleAndHeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue
Namespace Prefix: | nksh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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
Name: | nksh_ContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses
Namespace Prefix: | nksh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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
Name: | nksh_ContinuousUnrealizedLossPositionAggregateLosses
Namespace Prefix: | nksh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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
Name: | nksh_ContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Namespace Prefix: | nksh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition This item contains disclosure of the number of investment positions determined to be temporarily impaired. + References No definition available. + Details
Name: | nksh_NumberOfTemporarilyImpairedSecurities
Namespace Prefix: | nksh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition This item contains disclosure of the number of investment positions determined to be temporarily impaired in a continuous loss position for twelve months or more. + References No definition available. + Details
Name: | nksh_NumberOfTemporarilyImpairedSecuritiesGreaterThanTwelveMonths
Namespace Prefix: | nksh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Amount of the collateral pledged in support of federal home loan bank advances outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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 Reference 2: http://www.xbrl.org/2003/role/presentationRef -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 + Details
Name: | us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Investments which are not defined as or included in marketable (debt, equity, or other) securities whose use is restricted in whole or in part, generally by contractual agreements or regulatory requirements. For use in an unclassified balance sheet. + References No definition available. + Details
Name: | us-gaap_RestrictedInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis=us-gaap_FederalHomeLoanBankOfAtlantaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | dei_LegalEntityAxis=nksh_NationalBankOfBlacksburgMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=nksh_OtherSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |