XML 100 R85.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Note 16 - Fair Value Measurements - Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Securities available for sale | $ 331,387 | $ 304,282
Fair Value, Inputs, Level 1 [Member] |  |
Securities available for sale | 0 | 0
Fair Value, Inputs, Level 2 [Member] |  |
Securities available for sale | 331,387 | 304,282
Fair Value, Inputs, Level 3 [Member] |  |
Securities available for sale | 0 | 0
US Government Agencies Debt Securities [Member] |  |
Securities available for sale | 307,719 | 285,598
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Securities available for sale | 0 | 0
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Securities available for sale | 307,719 | 285,598
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Securities available for sale | 0 | 0
US States and Political Subdivisions Debt Securities [Member] |  |
Securities available for sale | 16,834 | 11,693
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Securities available for sale | 0 | 0
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Securities available for sale | 16,834 | 11,693
US States and Political Subdivisions Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Securities available for sale | 0 | 0
Collateralized Mortgage Backed Securities [Member] |  |
Securities available for sale | 659 | 930
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Securities available for sale | 0 | 0
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Securities available for sale | 659 | 930
Collateralized Mortgage Backed Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Securities available for sale | 0 | 0
Corporate Debt Securities [Member] |  |
Securities available for sale | 6,175 | 5,898
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Securities available for sale | 0 | 0
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Securities available for sale | 6,175 | 5,898
Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Securities available for sale | $ 0 | 0
Other Securities [Member] |  |
Securities available for sale |  | 163
Other Securities [Member] | Fair Value, Inputs, Level 1 [Member] |  |
Securities available for sale |  | 0
Other Securities [Member] | Fair Value, Inputs, Level 2 [Member] |  |
Securities available for sale |  | 163
Other Securities [Member] | Fair Value, Inputs, Level 3 [Member] |  |
Securities available for sale |  | $ 0

X
- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 5 -Subparagraph (aa) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26610-111562 + Details
Name: | us-gaap_AvailableForSaleSecurities
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
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=us-gaap_MortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_CorporateDebtSecuritiesMember
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: |