Property, Plant and Equipment (Narrative) (Detail) (USD $)	3 Months Ended	6 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012	Dec. 31, 2011
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 256,000	$ 262,000	$ 507,000	$ 520,000

The aggregate expense recognized in the current period that allocates the cost of long-lived tangible assets to periods that benefit from use of the assets.

No definition available.

Name:	nssc_DepreciationAmortizationOfPropertyPlantEquipment
Namespace Prefix:	nssc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration