XML 52 R42.htm IDEA: XBRL DOCUMENT
v3.22.1

Note 4 - Securities - Securities in a Continuous Loss Position (Details) - USD ($) $ in Thousands | Mar. 31, 2022 | Dec. 31, 2021
--- | --- | ---
Temporarily impaired securities, less than 12 months, fair value | $ 525,094 | $ 266,414
Temporarily impaired securities, less than 12 months unrealized loss | 25,715 | 4,922
Temporarily impaired securities, 12 months or more fair value | 114,273 | 51,999
Temporarily impaired securities, 12 months or more unrealized loss | 14,880 | 2,145
US Treasury Securities [Member] |  |
Temporarily impaired securities, less than 12 months, fair value | 964 |
Temporarily impaired securities, less than 12 months unrealized loss | 25 |
Temporarily impaired securities, 12 months or more fair value | 0 |
Temporarily impaired securities, 12 months or more unrealized loss | 0 |
US Government Agencies Debt Securities [Member] |  |
Temporarily impaired securities, less than 12 months, fair value | 238,220 | 201,650
Temporarily impaired securities, less than 12 months unrealized loss | 14,294 | 3,530
Temporarily impaired securities, 12 months or more fair value | 68,352 | 26,792
Temporarily impaired securities, 12 months or more unrealized loss | 8,570 | 1,180
US States and Political Subdivisions Debt Securities [Member] |  |
Temporarily impaired securities, less than 12 months, fair value | 120,206 | 50,659
Temporarily impaired securities, less than 12 months unrealized loss | 8,951 | 1,214
Temporarily impaired securities, 12 months or more fair value | 36,298 | 20,542
Temporarily impaired securities, 12 months or more unrealized loss | 5,850 | 793
Commercial Mortgage-Backed Securities [Member] |  |
Temporarily impaired securities, less than 12 months, fair value | 160,387 | 13,139
Temporarily impaired securities, less than 12 months unrealized loss | 2,262 | 141
Temporarily impaired securities, 12 months or more fair value | 9,623 | 4,665
Temporarily impaired securities, 12 months or more unrealized loss | 460 | 172
Corporate Debt Securities [Member] |  |
Temporarily impaired securities, less than 12 months, fair value | 5,317 | 966
Temporarily impaired securities, less than 12 months unrealized loss | 183 | 37
Temporarily impaired securities, 12 months or more fair value | 0 | 0
Temporarily impaired securities, 12 months or more unrealized loss | $ 0 | $ 0

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 have been in a loss position for less than twelve months for securities. + References No definition available. + Details
Name: | nksh_ContinuousUnrealizedLossPositionLessThan12MonthsAggregateLosses
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 less than twelve months. + References No definition available. + Details
Name: | nksh_ContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Namespace Prefix: | nksh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |