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v2.4.0.6

Consolidated Statements of Income (Parenthetical) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Interest Expense |  |  |
Threshold limit of time deposits, minimum | $ 100,000 | $ 100,000 | $ 100,000

X
- Definition Represents minimum threshold limit of time deposit for which interest to be recognized separately. + References No definition available. + Details
Name: | nksh_MinimumThresholdLimitOfTimeDeposits
Namespace Prefix: | nksh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_InterestExpenseTimeDepositsAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration