XML 52 R42.htm IDEA: XBRL DOCUMENT
v3.23.2

Note 3 - Securities (Details Textual) $ in Thousands | 3 Months Ended |
--- | --- | ---
Jun. 30, 2023 USD ($) | Mar. 31, 2023 USD ($) | Dec. 31, 2022 USD ($)
Deferred Tax Asset, Debt Securities, Available-for-Sale, Unrealized Loss | $ 19,112 |  | $ 21,644
Number of Temporarily Impaired Securities Greater than Twelve Months | 578 |  |
Continuous Unrealized Loss Position Aggregate Losses | $ 613,836 |  |
Available-for-sale Securities Sold, Book Value | 28,863 | $ 17,987 |
Realized Investment Gains (Losses) | (3,344) | $ 12 |
National Bank of Blacksburg [Member] | Federal Home Loan Bank of Atlanta [Member] |  |  |
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged | $ 633,617 |  |

X
- Definition Represents the book value of available-for-sale securities that had been sold. + References No definition available. + Details
Name: | nksh_AvailableForSaleSecuritiesSoldBookValue
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 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 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, before allocation of valuation allowance, of deferred tax asset attributable to deductible temporary difference from unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 740 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 6 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482685/740-10-50-6 + Details
Name: | us-gaap_DeferredTaxAssetsUnrealizedLossesOnAvailableforSaleSecuritiesGross
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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 -Topic 942 -SubTopic 470 -Name Accounting Standards Codification -Section 45 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org//1943274/2147480876/942-470-45-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org//1943274/2147480848/942-470-50-3 + Details
Name: | us-gaap_FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresCollateralPledged1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Amount of realized gain (loss) on investment. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 944 -SubTopic 220 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04(3)(a)) -Publisher FASB -URI https://asc.fasb.org//1943274/2147483586/944-220-S99-1 + Details
Name: | us-gaap_RealizedInvestmentGainsLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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

X
- Details
Name: | srt_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis=srt_FederalHomeLoanBankOfAtlantaMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |