Commitments and Contingencies - Additional Information (Details)	3 Months Ended
Sep. 30, 2021 USD ($) a agreement	Sep. 30, 2020 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease term	99 years
Annual minimum rent	$ 288,000
Operating Lease Payments	72,000	$ 72,000
Operating lease expense	$ 80,000	$ 79,000
Number of employment agreement \| agreement	2
Number of severance agreement \| agreement	1
Dominican Republic
Lessee, Lease, Description [Line Items]
Area of Land \| a	4
Employment agreement \| CEO
Lessee, Lease, Description [Line Items]
Annual salary commitment	$ 838,000
Termination pay commitment rate applied to the average of the prior five calendar years compensation	299.00%
Employment agreement \| SVP of Engineering
Lessee, Lease, Description [Line Items]
Annual salary commitment	$ 347,000

The amount of annual cost the entity is obligated to pay each year for rent.

No definition available.

Name:	nssc_AnnualMinimumRent
Namespace Prefix:	nssc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of salary the entity is obligated to pay each year pursuant to terms of one or more agreements with employees.

+ References

No definition available.

+ Details

Name:	nssc_CommitmentAnnualSalary
Namespace Prefix:	nssc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The rate applied to the most recent 5-year average of annual salaries, as defined, to calculate termination pay the entity has committed to pay under specified circumstances.

+ References

No definition available.

+ Details

Name:	nssc_CommitmentTerminationPay
Namespace Prefix:	nssc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of employment agreement.

+ References

No definition available.

+ Details

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

- Definition

Number of severance agreement.

+ References

No definition available.

+ Details

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

- Definition

Area of land held.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfLand
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
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_LesseeLeaseDescriptionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918673-209980

+ Details

Name:	us-gaap_LesseeOperatingLeaseTermOfContract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of operating lease expense. Excludes sublease income.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918638-209977

+ Details

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

- Definition

Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=121603541&loc=SL77918643-209977

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (g)(1)
-URI http://asc.fasb.org/extlink&oid=121609121&loc=SL77918686-209980

+ Details

Name:	us-gaap_OperatingLeasePayments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	srt_StatementGeographicalAxis=country_DO
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_OtherCommitmentsAxis=us-gaap_EmploymentContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=srt_ChiefExecutiveOfficerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=srt_VicePresidentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: