The amount of early lease relocation expense.

No definition available.

Name:	ngvc_EarlyLeaseRelocationExpense
Namespace Prefix:	ngvc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The amount of increase (decrease) to the present value of lessee's discounted obligation for lease payments from finance lease during the period resulting from the purchase of previous leases.

+ References

No definition available.

+ Details

Name:	ngvc_FinanceLeaseLiabilityIncreaseDecreaseInPeriodPurchasesOfPreviousLeases
Namespace Prefix:	ngvc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of lessee's undiscounted obligation for lease payments for operating lease not yet commenced.

+ References

No definition available.

+ Details

Name:	ngvc_LesseeOperatingLeaseLeaseNotYetCommencedMinimumLeasePayments
Namespace Prefix:	ngvc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents the number of operating leases, leased by the entity.

+ References

No definition available.

+ Details

Name:	ngvc_NumberOfOperatingLeases
Namespace Prefix:	ngvc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The increase (decrease) of the present value of lessee's discounted obligation for lease payments from operating lease resulting from purchases of previous leases.

+ References

No definition available.

+ Details

Name:	ngvc_OperatingLeaseLiabilityIncreaseDecreaseInPeriodPurchasesOfPreviousLeases
Namespace Prefix:	ngvc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents write-off operating lease liability.

+ References

No definition available.

+ Details

Name:	ngvc_OperatingLeaseLiabilityWriteoff
Namespace Prefix:	ngvc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of reclassification of finance lease assets into long-lived, physical assets used in the normal conduct of business and not intended for resale.

+ References

No definition available.

+ Details

Name:	ngvc_PropertyPlantAndEquipmentAdditionsReclassificationOfFinanceLeaseAssets
Namespace Prefix:	ngvc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of reclassification of operating lease assets into long-lived, physical assets used in the normal conduct of business and not intended for resale.

+ References

No definition available.

+ Details

Name:	ngvc_PropertyPlantAndEquipmentAdditionsReclassificationOfOperatingLeaseAssets
Namespace Prefix:	ngvc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Term of lessee's operating lease renewal, 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
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478964/842-20-50-3

+ Details

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

- 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

+ 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
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 4
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-4

+ Details

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

- Definition

Amount of loss from impairment of right-of-use asset from operating lease.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 6
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479365/842-20-25-6

+ Details

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

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

+ Details

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

- Definition

Present value of lessee's discounted obligation for lease payments from operating lease, classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 8
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147483467/210-10-45-8

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

+ Details

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

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 842
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479041/842-20-45-1

+ Details

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

- Details

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

- Details

Name:	srt_CounterpartyNameAxis=ngvc_ChaletMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=ngvc_IselyFamilyLandTrustLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=ngvc_FTVCLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 7 - Leases (Details Textual) $ in Thousands	3 Months Ended		9 Months Ended
Note 7 - Leases (Details Textual) $ in Thousands	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Sep. 30, 2025 USD ($)
Operating Lease, Right-of-Use Asset	$ 251,627		$ 251,627		$ 259,586
Operating Lease, Liability	275,456		275,456
Operating Lease, Liability, Current	37,728		37,728		$ 36,495
Operating Lease Liability, Increase (Decrease) in Period, Purchases of Previous Leases			(500)
Finance Lease Liability, Increase (Decrease) in Period, Purchases of Previous Leases			(1,100)
Property, Plant and Equipment, Additions, Reclassification of Operating Lease Assets			(100)
Property, Plant and Equipment, Additions, Reclassification of Finance Lease Assets			(300)
Operating Lease, Impairment Loss				$ 100
Operating Lease, Liability, Write-off				100
Early Lease Relocation Expense				100
Lessee, Operating Lease, Lease Not yet Commenced, Minimum Lease Payments	6,000		6,000
Related Party [Member]
Operating Lease, Right-of-Use Asset	9,600		9,600
Operating Lease, Liability	9,800		9,800
Operating Lease, Liability, Current	800		800
Operating Lease, Expense	$ 300	$ 300	$ 1,000	$ 900
Chalet [Member]
Number of Operating Leases	5		5
Isely Family Land Trust LLC [Member]
Number of Operating Leases	1		1
FTVC, LLC [Member]
Number of Operating Leases	1		1
Minimum [Member]
Lessee, Operating Lease, Term of Contract	10 years		10 years
Lessee, Operating Lease, Renewal Term	5 years		5 years
Maximum [Member]
Lessee, Operating Lease, Term of Contract	25 years		25 years
Lessee, Operating Lease, Renewal Term	10 years		10 years