Long-Term Debt (Narrative) (Detail) (USD $)	9 Months Ended
Mar. 31, 2015
Term loan expiring June 2019 [Member]
Debt Instrument [Line Items]
Initial amount of loan	$ 6,000,000
Number of required loan repayments from inception	28
Quarterly principal repayment amount	75,000
Payoff amount at maturity	3,900,000
Debt Instrument, Frequency of Periodic Payment	quarterly
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
Debt Instrument, Frequency of Periodic Payment	quarterly
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]
Debt Instrument [Line Items]
Debt Instrument, Description of Variable Rate Basis	prime
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%
Debt Instrument, Description of Variable Rate Basis	LIBOR
Third Amended and Restated Credit Agreement [Member] \| Variable Interest Rate Option One [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Interest rate over the reference rate	2.75%
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%
Revolving line of credit expiring June 2017 [Member]
Debt Instrument [Line Items]
Revolving credit loan facility, maximum borrowing capacity	$ 11,000,000

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

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentDescriptionOfVariableRateBasis
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 2: 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

+ Details

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

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ 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 SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 3: 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_DebtInstrumentFrequencyOfPeriodicPayment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- 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

+ 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_DebtInstrumentAxis=nssc_ThirdAmendedRestatedCreditAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_LongtermDebtTypeAxis=nssc_TermLoanJune2019Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: