Long-Term Debt - Additional Information (Details)	12 Months Ended
Jun. 30, 2019 USD ($)
Revolving line of credit expiring June 2021 [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	1.15%
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	2.00%
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%

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.

No definition available.

+ Details

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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

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Namespace Prefix:	us-gaap_
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Period Type:	duration

- 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

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- 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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Details

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- Details

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- Details

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- Details

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