Leases (Narrative) (Details) (USD $) In Billions, unless otherwise specified	12 Months Ended
Sep. 30, 2012 Y
Leases [Abstract]
Lease renewal option as lessee, minimum (in years)	5
Lease renewal option as lessee, maximum (in years)	20
Minimum sublease rents	$ 1.1
Lease term (in years)	20
Lease renewal option as lessor, minimum (in years)	5
Lease renewal option as lessor, maximum (in years)	20

The maximum length of time generally for which a lease can be renewed at the option of the company.

No definition available.

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Period Type:	duration

- Definition

The maximum length of time generally for which a lease can be renewed at the option of the company.

+ References

No definition available.

+ Details

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Namespace Prefix:	jack_
Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum length of time generally for which a lease can be renewed at the option of the company.

+ References

No definition available.

+ Details

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Namespace Prefix:	jack_
Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum length of time generally for which a lease can be renewed at the option of the company.

+ References

No definition available.

+ Details

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Namespace Prefix:	jack_
Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	duration

- Definition

The general term of our leases.

+ References

No definition available.

+ Details

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Namespace Prefix:	jack_
Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	duration

- Details

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Period Type:	duration

- Definition

Contractually required future rental payments receivable on noncancelable subleasing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 13

-Paragraph 16

-Subparagraph b(ii)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant