Amount of the effect of a change in accounting principle on other assets.

No definition available.

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

- Definition

Amount of the effect of a change in accounting principle on receivables.

+ References

No definition available.

+ Details

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

- Definition

Amount of the effect of a change in accounting principle on refund liabilities.

+ References

No definition available.

+ Details

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

- Definition

Amount of the effect of a change in accounting principle on income tax expense benefit

+ References

No definition available.

+ Details

Name:	nssc_NewAccountingPronouncementOrChangeInAccountingPrincipleIncomeTaxExpenseBenefit
Namespace Prefix:	nssc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6351-108592

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13531-108611

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118260190&loc=d3e13537-108611

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=99393423&loc=d3e6404-108592

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of right to recover product from customer on settling refund liability.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 55
-Paragraph 27
-URI http://asc.fasb.org/extlink&oid=118944142&loc=SL49130611-203046-203046

+ Details

Name:	us-gaap_ContractWithCustomerRightToRecoverProduct
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)(3)
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22583-107794

+ Details

Name:	us-gaap_NewAccountingPronouncementOrChangeInAccountingPrincipleCumulativeEffectOfChangeOnEquityOrNetAssets1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_RevenueFromContractWithCustomerProductAndServiceBenchmarkMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ChangeInAccountingEstimateByTypeAxis=us-gaap_SalesReturnsAndAllowancesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Revenue Recognition and Contracts with Customers - Additional Information (Details) - USD ($)		3 Months Ended
	Jul. 01, 2018	Sep. 30, 2019	Sep. 30, 2018
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	$ 719,000
New Accounting Pronouncement or Change in Accounting Principle Income Tax Expense Benefit	191,000
New Accounting Pronouncement or Change in Accounting Principle Effect of Change In Other Assets	716,000
Return-related assets		$ 737,000
New Accounting Pronouncement or Change in Accounting Principle Effect of Change on Receivables		$ 3,181,000
New Accounting Pronouncement or Change in Accounting Principle Effect of Change on Refund Liabilities	$ 1,627,000
Sales Revenue, Product Line [Member]
Concentration Risk, Percentage		8.00%
Sales Returns and Allowances [Member]
Concentration Risk, Percentage			9.00%