Acquisition of Business (Narrative) (Detail) (G. Marks Hardware, Inc [Member], USD $) In Thousands, unless otherwise specified	Aug. 18, 2008
G. Marks Hardware, Inc [Member]
Business Acquisition [Line Items]
Business acquisition, cost of acquired entity, purchase price excluding direct acquisition costs	$ 25,200
Business acquisition, cost of acquired entity, repayment of acquiree bank debt	$ 1,000

The cost of the acquired entity including the cash paid to shareholders of acquired entities, fair value of debt and equity securities issued to shareholders of acquired entities, and the fair value of the liabilities assumed. Excludes direct costs of the acquisition.

No definition available.

Name:	nssc_BusinessAcquisitionCostOfAcquiredEntityPurchasePriceExcludingAcquisitionCosts
Namespace Prefix:	nssc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant