The maximum number of days consumer loans are past due for losses on such loans to be written off.

No definition available.

Name:	nksh_MaximumNumberOfDaysConsumerLoansArePastDueForLossesToBeChargedOff
Namespace Prefix:	nksh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum number of days consumer loans are past due for losses on such loans to be written off.

+ References

No definition available.

+ Details

Name:	nksh_MinimumNumberOfDaysConsumerLoansArePastDueForLossesToBeChargedOff
Namespace Prefix:	nksh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum number of days of no loan payments due to loan modification for the loan to be placed on nonaccrual.

+ References

No definition available.

+ Details

Name:	nksh_MinimumNumberOfDaysOfDiscontinuedLoanPaymentsForModifiedLoanToBePlacedOnNonaccrual
Namespace Prefix:	nksh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	nksh_Note1SummaryofSignificantAccountingPoliciesDetailsLineItems
Namespace Prefix:	nksh_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of days loans secured by residential or commercial real estate are past due for losses to be written off.

+ References

No definition available.

+ Details

Name:	nksh_NumberOfDaysLoansSecuredByResidentialOrCommercialRealEstateArePastDueForLossesToBeChargedOff
Namespace Prefix:	nksh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number days of delinquent loans for interest accrual to be discontinued.

+ References

No definition available.

+ Details

Name:	nksh_NumberOfDaysOfDelinquentLoansNonaccrualOfInterest
Namespace Prefix:	nksh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of days that all loans and receivables are not received within certain number of days after the payment due date or statement date.

+ References

No definition available.

+ Details

Name:	nksh_NumberOfDaysPastDue
Namespace Prefix:	nksh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Minimum period of time between issuance of loans commitment and closing and sale of loans.

+ References

No definition available.

+ Details

Name:	nksh_PeriodOfTimeBetweenIssuanceOfLoanCommitmentAndClosingAndSaleOfLoansLowerRange
Namespace Prefix:	nksh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Maximum period of time between issuance of loans commitment and closing and sale of loans.

+ References

No definition available.

+ Details

Name:	nksh_PeriodOfTimeBetweenIssuanceOfLoanCommitmentsAndClosingAndSaleOfLoansUpperRang
Namespace Prefix:	nksh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

This is threshold for designation to impaired status for loan relationship that are non accrual, significantly past due, display credit weakness or are TDR.

+ References

No definition available.

+ Details

Name:	nksh_ThresholdForDesignationToImpairedStatus
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount charged to advertising expense for the period, which are expenses incurred with the objective of increasing revenue for a specified brand, product or product line.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 720

-SubTopic 35

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6420018&loc=d3e36677-107848

+ Details

Name:	us-gaap_AdvertisingExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 260

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Antidilution

-URI http://asc.fasb.org/extlink&oid=6505113

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Diluted Earnings Per Share

-URI http://asc.fasb.org/extlink&oid=6510752

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Contingent Stock Agreement

-URI http://asc.fasb.org/extlink&oid=6508534

+ Details

Name:	us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of loss from the write-down of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13854-109267

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13777-109266

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 350

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

+ Details

Name:	us-gaap_GoodwillImpairmentLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

+ References

No definition available.

+ Details

Name:	us-gaap_MinorityInterestOwnershipPercentageByParent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertyPlantAndEquipmentUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_ComputerEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_FurnitureAndFixturesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 1 - Summary of Significant Accounting Policies (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items]
Number of Days of Delinquent Loans Nonaccrual of Interest	90 days
Minimum Number of Days of Discontinued Loan Payments for Modified Loan to Be Placed On Nonaccrual	90 days
Number of Days Past Due	30 days
Threshold for Designation to Impaired Status (in Dollars)	$ 250,000
Minimum Number of Days Consumer Loans Are Past Due for Losses to Be Charged-off	120 days
Maximum Number of Days Consumer Loans Are Past Due for Losses to Be Charged-off	180 days
Number of Days Loans Secured by Residential Or Commercial Real Estate Are Past Due for Losses to Be Charged Off	180 days
Period of Time Between Issuance of Loan Commitment and Closing and Sale of Loans, Lower Range	30 days
Period of Time Between Issuance of Loan Commitments and Closing and Sale of Loans Upper Range	60 days
Goodwill, Impairment Loss (in Dollars)	0us-gaap_GoodwillImpairmentLoss	0us-gaap_GoodwillImpairmentLoss	0us-gaap_GoodwillImpairmentLoss
Noncontrolling Interest, Ownership Percentage by Parent	100.00%
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in Shares)	0	0	0
Advertising Expense (in Dollars)	$ 174us-gaap_AdvertisingExpense	$ 194us-gaap_AdvertisingExpense	$ 169us-gaap_AdvertisingExpense
Building [Member]
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items]
Property, Plant and Equipment, Useful Life	40 years
Furniture and Fixtures [Member] \| Minimum [Member]
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Furniture and Fixtures [Member] \| Maximum [Member]
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items]
Property, Plant and Equipment, Useful Life	10 years
Computer Equipment [Member]
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items]
Property, Plant and Equipment, Useful Life	3 years
Minimum [Member]
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items]
Finite-Lived Intangible Asset, Useful Life	10 years
Maximum [Member]
Note 1 - Summary of Significant Accounting Policies (Details) [Line Items]
Finite-Lived Intangible Asset, Useful Life	12 years