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v2.4.0.6

401(k) Plan (Narrative) (Detail) (USD $) | 3 Months Ended | 6 Months Ended
--- | --- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2012 | Dec. 31, 2011
Napco 401 (k) Plan [Member] |  |  |  |
Schedule of Deferred Compensation Plans [Line Items] |  |  |  |
Deferred compensation plan expense | $ 23,000 | $ 0 | $ 44,000 | $ 0
Marks 401 (k) Plan [Member] |  |  |  |
Schedule of Deferred Compensation Plans [Line Items] |  |  |  |
Deferred compensation plan expense | $ 1,000 | $ 0 | $ 2,000 | $ 0

X
- Definition The compensation expense recognized during the period pertaining to a deferred compensation arrangement. + References No definition available. + Details
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Namespace Prefix: | nssc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | nssc_ScheduleOfDeferredCompensationPlansLineItems
Namespace Prefix: | nssc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration