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Stock Options (Narrative) (Detail) (USD $)
3 Months Ended 9 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Mar. 31, 2015
Mar. 31, 2014
Jun. 30, 2014
Jun. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Cash received from option exercises     $ 0us-gaap_ProceedsFromStockOptionsExercised $ 25,000us-gaap_ProceedsFromStockOptionsExercised    
Allocated Share Based Compensation Expense 0us-gaap_AllocatedShareBasedCompensationExpense 10,000us-gaap_AllocatedShareBasedCompensationExpense 101,000us-gaap_AllocatedShareBasedCompensationExpense 17,000us-gaap_AllocatedShareBasedCompensationExpense    
Share based Compensation Cost Effect On Earnings Per Share Basic And Diluted $ 0.00nssc_ShareBasedCompensationCostEffectOnEarningsPerShareBasicAndDiluted $ 0.00nssc_ShareBasedCompensationCostEffectOnEarningsPerShareBasicAndDiluted $ 0.00nssc_ShareBasedCompensationCostEffectOnEarningsPerShareBasicAndDiluted $ 0.00nssc_ShareBasedCompensationCostEffectOnEarningsPerShareBasicAndDiluted    
Employee 2012 Stock Option Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of shares authorized for issuance under the plan 950,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
  950,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
     
Percentage Applied To Market Price To Set Grant Price For Grantee Owning Ten Percent Or More Of Entity Common Stock Outstanding     110.00%nssc_PercentageAppliedToMarketPriceToSetGrantPriceForGranteeOwningTenPercentOrMoreOfEntityCommonStockOutstanding
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
     
Term of stock option awards     10 years      
Annual rate at which share-based compensation awards vest     20.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
     
Number of stock options, granted     44,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
78,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
   
Number of stock options, exercisable 27,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
15,700us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
27,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
15,700us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
   
Number of stock options available for grant 837,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
  837,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
     
Unearned stock-based compensation cost related to non-vested awards 260,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
  260,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
     
Fair value of stock options that vested during the period 0us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
0us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
41,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
60,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
   
Number of shares outstanding, end of period 112,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
78,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
112,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
78,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
78,500us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
Number of stock options, exercised     0us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
0us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_PlanNameAxis
= nssc_Employee2012StockOptionPlanMember
   
Common Stock, Voting Rights     Any plan participant who was granted ISOs and possessed more than 10% of the voting rights of the Company's outstanding common stock      
NonEmployee 2012 Stock Option Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of shares authorized for issuance under the plan 50,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
  50,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
     
Term of stock option awards     10 years      
Annual rate at which share-based compensation awards vest     20.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
     
Number of stock options, granted     10,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
25,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
   
Number of stock options, exercisable 12,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
5,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
12,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
5,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
   
Number of stock options available for grant 15,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
  15,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
     
Unearned stock-based compensation cost related to non-vested awards 72,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
  72,000us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
     
Fair value of stock options that vested during the period 0us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
0us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
6,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
22,000us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsVestedInPeriodFairValue1
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
   
Number of shares outstanding, end of period 35,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
25,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
35,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
25,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
25,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
Number of stock options, exercised     0us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
0us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_PlanNameAxis
= nssc_Nonemployee2012StockOptionPlanMember
   
2002 Employee Stock Option Plan [Member]            
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]            
Number of shares authorized for issuance under the plan 1,836,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
  1,836,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
     
Percentage Applied To Market Price To Set Grant Price For Grantee Owning Ten Percent Or More Of Entity Common Stock Outstanding     110.00%nssc_PercentageAppliedToMarketPriceToSetGrantPriceForGranteeOwningTenPercentOrMoreOfEntityCommonStockOutstanding
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
     
Term of stock option awards     10 years      
Annual rate at which share-based compensation awards vest     20.00%us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
     
Number of stock options, exercisable 264,750us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
  264,750us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
     
Tax benefit from stock option exercise     0us-gaap_DeferredTaxExpenseFromStockOptionsExercised
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
0us-gaap_DeferredTaxExpenseFromStockOptionsExercised
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
   
Cash received from option exercises     $ 0us-gaap_ProceedsFromStockOptionsExercised
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
$ 25,650us-gaap_ProceedsFromStockOptionsExercised
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
   
Number of shares outstanding, end of period 1,471,480us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
  1,471,480us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
     
Number of stock options, exercised     0us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
337,600us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
   
Stock Issued During Period, Shares, New Issues     324,100us-gaap_StockIssuedDuringPeriodSharesNewIssues
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
     
Conversion of Stock, Shares Issued       164,859us-gaap_ConversionOfStockSharesIssued1
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember
   
Common Stock Retired       85,170us-gaap_StockRepurchasedAndRetiredDuringPeriodShares
/ us-gaap_PlanNameAxis
= nssc_Employee2002StockOptionPlanMember