Recent Accounting Pronouncements (Details)	6 Months Ended
Jun. 30, 2012
Recent Accounting Pronouncements [Abstract]
Probability in percentage determining threshold for performing two step goodwill impairment test (in hundredths)	50.00%

Refers to probability in percentage determining threshold for performing two step goodwill impairment test.

No definition available.

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