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Supplementary Balance Sheet Information (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
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Sep. 25, 2021 | Sep. 26, 2020 | Sep. 28, 2019
Supplementary Balance Sheet Information [Abstract] |  |  |
Employee insurance expense | $ 35.5 | $ 38.5 | $ 37.3

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- References No definition available. + Details
Name: | imkta_SupplementaryBalanceSheetInformationAbstract
Namespace Prefix: | imkta_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition The expense in the period incurred with respect to protection provided by insurance entities against risks other than risks associated with production (which are allocated to cost of sales). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.4) -URI http://asc.fasb.org/extlink&oid=120395209&loc=SL114868664-224227 + Details
Name: | us-gaap_GeneralInsuranceExpense
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration