Collection Period for Marketing Fees

No definition available.

Name:	jack_CollectionPeriodForMarketingFees
Namespace Prefix:	jack_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

ContractualContributionsTowardsAdvertisingCostsPercentageOfSales [Line Items]

+ References

No definition available.

+ Details

Name:	jack_ContractualContributionsTowardsAdvertisingCostsPercentageOfSales
Namespace Prefix:	jack_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Exit-related Lease Liabilities

+ References

No definition available.

+ Details

Name:	jack_ExitRelatedLeaseLiabilities
Namespace Prefix:	jack_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Incremental Corporate Advertising Contributions

+ References

No definition available.

+ Details

Name:	jack_IncrementalCorporateAdvertisingContributions
Namespace Prefix:	jack_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22663-107794

+ Details

Name:	us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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.

+ References

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

+ Details

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

- 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)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

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

+ 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=116634182&loc=SL114868664-224227

+ Details

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

- 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.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of restaurants.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfRestaurants
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- 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.

+ 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 210.5-02.24)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Definition

Amount of cash restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=98513485&loc=SL98516268-108586

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(1)(a))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(2))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

+ Details

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

- 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

- Details

Name:	srt_StatementScenarioAxis=srt_ScenarioForecastMember
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:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_StatementOperatingActivitiesSegmentAxis=us-gaap_EntityOperatedUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementOperatingActivitiesSegmentAxis=us-gaap_FranchisedUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Basis Of Presentation (Details) $ in Thousands		1 Months Ended		3 Months Ended			5 Months Ended	6 Months Ended
Basis Of Presentation (Details) $ in Thousands	Sep. 30, 2019 USD ($)	Apr. 30, 2020	Mar. 31, 2020	Dec. 31, 2020	Apr. 12, 2020 USD ($) restaurant	Apr. 14, 2019 USD ($) restaurant	Feb. 29, 2020	Apr. 12, 2020 USD ($) restaurant segment	Apr. 14, 2019 USD ($) restaurant	Sep. 29, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of restaurants \| restaurant					2,246	2,240		2,246	2,240
Number of operating segments \| segment								1
Contractual obligation (percent)			4.00%				5.00%
Collection period for marketing fees			24 months
Incremental Corporate Advertising Contributions								$ 0	$ 2,000
Marketing and advertising expense					$ 3,500	$ 3,900		8,900	11,100
Restricted cash					37,000			37,000		$ 26,000
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	$ (2,900)				$ 0	$ 0		$ (2,870)	$ (37,330)
Forecast
Segment Reporting Information [Line Items]
Collection period for marketing fees				3 months
Minimum \| Subsequent Event
Segment Reporting Information [Line Items]
Contractual obligation (percent)		2.00%
Maximum \| Subsequent Event
Segment Reporting Information [Line Items]
Contractual obligation (percent)		4.00%
Entity Operated Units
Segment Reporting Information [Line Items]
Number of restaurants \| restaurant					144	137		144	137
Franchised Units
Segment Reporting Information [Line Items]
Number of restaurants \| restaurant					2,102	2,103		2,102	2,103