Note 2 - Loans and Allowance for Credit Losses - Loans Past Due 90 Days or More and Impaired Loans (Details)	Jun. 30, 2023	Dec. 31, 2022	Jun. 30, 2022
Ratio of ACLL to nonaccrual loans	345.56%	288.90%	270.86%
Ratio of loans past due 90 days or more and still accruing to loans, net of unearned income and deferred fees and costs	0.00%	0.00%	0.00%

Represents ratio of loans past due 90 days or more and still accruing to loans, net of unearned income and deferred fees.

No definition available.

Name:	nksh_RatioOfLoansPastDue90DaysOrMoreAndStillAccruingToLoans
Namespace Prefix:	nksh_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant