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Business and Credit Concentrations (Detail) (Accounts receivable benchmark [Member]) | Dec. 31, 2012 Customer | Jun. 30, 2012
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Accounts receivable benchmark [Member] |  |
Concentration Risk [Line Items] |  |
Percentage that a major customer's balance is to total accounts receivable | 11.00% | 15.00%
Percentage that the sum of significant customers' balances are to total accounts receivable, number of customers | 1 |

X
- Definition The number of customers included in a calculation of the ratio of the aggregate balances due from more than one significant customer over total accounts receivable. + References No definition available. + Details
Name: | nssc_PercentageOfSignificantCustomerBalancesToTotalAccountsReceivableNumberOfCustomers
Namespace Prefix: | nssc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The ratio of the balance due from a significant customer over total accounts receivable. + References No definition available. + Details
Name: | nssc_PercentageOfSingleSignificantCustomerBalanceToTotalAccountsReceivables
Namespace Prefix: | nssc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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