Basis Of Presentation (Details) $ in Thousands		4 Months Ended
Sep. 30, 2019 USD ($)	Jan. 19, 2020 USD ($) restaurant segment	Jan. 20, 2019 USD ($) restaurant
Segment Reporting Information [Line Items]
Number of restaurants \| restaurant		2,244	2,241
Number of operating segments \| segment		1
Contractual obligation (percent)		5.00%
Incremental Corporate Advertising Contributions			$ 2,000
Marketing and advertising expense		$ 5,300	7,200
Straight-line rent accrual	$ 29,000
Unfavorable lease liabilities	2,100
Exit-related lease liabilities	19,400
Favorable lease assets	400
Cumulative-effect from a change in accounting principle	$ (2,870)		$ (37,330)
Entity Operated Units
Segment Reporting Information [Line Items]
Number of restaurants \| restaurant		137	137
Franchised Units
Segment Reporting Information [Line Items]
Number of restaurants \| restaurant		2,107	2,104

ContractualContributionsTowardsAdvertisingCostsPercentageOfSales [Line Items]

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- Definition

Exit-related Lease Liabilities

+ References

No definition available.

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- Definition

Incremental Corporate Advertising Contributions

+ References

No definition available.

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Namespace Prefix:	jack_
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- Definition

Amount of the cumulative effect on retained earnings net of related income tax effect.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
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- Definition

The cumulative difference between the rental payments required by a lease agreement and the rental income or expense recognized on a straight-line basis, or other systematic and rational basis more representative of the time pattern in which use or benefit is granted or derived from the leased property, expected to be recognized in income or expense over the term of the leased property by the lessor or lessee, respectively.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=77902458&loc=d3e39896-112707

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- Definition

This element represents the identifiable intangible asset established upon acquisition based on a favorable difference between the terms of an acquired lease and the current market terms for that lease at the acquisition date.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.15)
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- Definition

The total expense recognized in the period for promotion, public relations, and brand or product advertising.

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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)
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- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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- Definition

Represents the number of restaurants.

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No definition available.

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- Definition

This element represents a liability associated with the acquisition of an off-market lease when the terms of the lease are unfavorable to the market terms for the lease at the date of acquisition.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section S99
-Paragraph 1
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- 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.

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