Business and Credit Concentrations (Detail) (Accounts receivable benchmark [Member])	Sep. 30, 2012 Item	Jun. 30, 2012
Accounts receivable benchmark [Member]
Concentration Risk [Line Items]
Percentage that a major customer's balance is to total accounts receivable	11.00%	15.00%
Percentage that the sum of significant customers' balances are to total accounts receivable	22.00%
Percentage that the sum of significant customers' balances are to total accounts receivable, number of customers	2

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