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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

X
- Definition 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. + References No definition available. + Details
Name: | nssc_DepreciationAmortizationOfPropertyPlantEquipment
Namespace Prefix: | nssc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration