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Note 5 - Allowance for Loan Losses, Nonperforming Assets and Impaired Loans (Details) - Ratios of Allowance for Loan Losses	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Ratios of Allowance for Loan Losses [Abstract]
Ratio of allowance for loan losses to the end of period loans, net of unearned income and deferred fees	1.34%	1.36%
Ratio of net charge-offs to average loans, net of unearned income and deferred fees	0.32%	0.27%

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- Definition

Represents ratio of allowance for loan losses to the end of period loans, net of unearned income and deferred fees.

+ References

No definition available.

+ Details

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X

- Definition

Represents ratio of net charge-offs to average loans, net of unearned income and deferred fees.

+ References

No definition available.

+ Details

Name:	nksh_RatioOfNetChargeOffsToAverageLoans
Namespace Prefix:	nksh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

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- References

No definition available.

+ Details

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Namespace Prefix:	nksh_
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