Business and Credit Concentrations (Detail) (Accounts receivable benchmark [Member])	Jun. 30, 2012	Jun. 30, 2011
Accounts receivable benchmark [Member]
Concentration Risk [Line Items]
Percentage that a major customer's balance is to total accounts receivable	15.00%	17.00%

The ratio of the balance due from a significant customer over total accounts receivable.

No definition available.

Name:	nssc_PercentageOfSingleSignificantCustomerBalanceToTotalAccountsReceivables
Namespace Prefix:	nssc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant