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Discontinued Operations (Lease Guarantee Details) (Details) | 12 Months Ended
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Sep. 27, 2020 USD ($)
Lease Guarantee [Abstract] |
Contractual obligation | $ 29,800,000
Qdoba guaranteed leases, remaining term | 15 years
Accrued amount related to guarantees | $ 0

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- Definition Lease Guarantee [Abstract] + References No definition available. + Details
Name: | jack_LeaseGuaranteeAbstract
Namespace Prefix: | jack_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Lessee, Guaranteed Leases, Remaining Term + References No definition available. + Details
Name: | jack_LesseeGuaranteedLeasesRemainingTerm
Namespace Prefix: | jack_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments. + References No definition available. + Details
Name: | us-gaap_ContractualObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 460 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=118943654&loc=d3e12069-110248 + Details
Name: | us-gaap_GuaranteeObligationsCurrentCarryingValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant