Long-Term Debt (Narrative) (Detail)	6 Months Ended
Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Initial amount of loan	$ 6,000,000
Number of required loan repayments from inception	28
Term loan expiring June 2017 [Member]
Debt Instrument [Line Items]
Initial amount of loan	$ 6,500,000
Number of required loan repayments from inception	20
Quarterly principal repayment amount	$ 325,000
Revolving line of credit expiring June 2017 [Member]
Debt Instrument [Line Items]
Revolving credit loan facility, maximum borrowing capacity	$ 11,000,000
Third Amended and Restated Credit Agreement [Member]
Debt Instrument [Line Items]
Percentage of common stock of foreign subsidiaries pledged as collateral	65.00%
Third Amended and Restated Credit Agreement [Member] \| Variable Interest Rate Option One [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest rate over the reference rate	1.50%
Third Amended and Restated Credit Agreement [Member] \| Variable Interest Rate Option Two [Member]
Debt Instrument [Line Items]
Interest rate over the reference rate	0.25%
Third Amended and Restated Credit Agreement [Member] \| Variable Interest Rate Option Two [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate over the reference rate	2.75%
Term Loan Quarterly Payments [Member]
Debt Instrument [Line Items]
Quarterly principal repayment amount	$ 75,000
Payoff amount at maturity	$ 3,900,000

The number of repayments a borrower is required to make at a specified frequency measured from loan inception.

No definition available.

Name:	nssc_NumberOfRequiredDebtRepaymentsFromInception
Namespace Prefix:	nssc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of the common stock of the Company's foreign subsidiaries that has been pledged to secure the Company's obligations under certain debt agreements.

+ References

No definition available.

+ Details

Name:	nssc_PercentageOfCapitalStockOfForeignSubsidiariesPledgedAsCollateral
Namespace Prefix:	nssc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of the required periodic payments including both interest and principal payments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

+ Details

Name:	us-gaap_DebtInstrumentPeriodicPayment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of payment greater than the preceding installment payments to be paid at final maturity date of debt.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

Name:	us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LongtermDebtTypeAxis=nssc_TermLoanJune2017Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_DomesticLineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nssc_ThirdAmendedRestatedCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=nssc_VariableInterestRateOptionOneMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VariableRateAxis=nssc_VariableInterestRateOptionTwoMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=nssc_TermLoanQuarterlyPaymentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: