Consolidated Statements of Income (Unaudited) (Parentheticals) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2014	Mar. 31, 2013
Threshold limit of time deposits, minimum	$ 100	$ 100

Represents minimum threshold limit of time deposit for which interest to be recognized separately.

No definition available.

Name:	nksh_MinimumThresholdLimitOfTimeDeposits
Namespace Prefix:	nksh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration