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Segment Information (Narrative) (Details) $ in Millions	3 Months Ended
	Dec. 28, 2019 USD ($) segment	Dec. 29, 2018 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments | segment	1
Fluid dairy [Member]
Segment Reporting Information [Line Items]
Sales eliminated in consolidation | $	$ 11.5	$ 11.0

X

- Definition

Intercompany eliminations.

+ References

No definition available.

+ Details

Name:	imkta_IntercompanyEliminations
Namespace Prefix:	imkta_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- 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_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=imkta_FluidDairyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: