Business and Credit Concentrations (Narrative) (Detail)	Dec. 31, 2014	Jun. 30, 2014
Concentration Risk [Line Items]
Percentage that a major customer's balance is to total accounts receivable	23.00%	12.00%
Percentage that the sum of significant customers balances are to total accounts receivable number of customers	2	1

The number of customers included in a calculation of the ratio of the aggregate balances due from more than one significant customer over total accounts receivable.

No definition available.

Name:	nssc_PercentageOfSignificantCustomerBalancesToTotalAccountsReceivableNumberOfCustomers
Namespace Prefix:	nssc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant