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Network
2411406 - Disclosure - Retirement Plans (Determining The Present Values Of Benefit Obligations And Net Periodic Benefit Costs) (Details)
(http://www.jackinthebox.com/role/RetirementPlansDeterminingPresentValuesOfBenefitObligationsAndNetPeriodicBenefitCostsDetails)
TableSchedule of Defined Benefit Plans Disclosures [Table]
Slicers (applies to each fact value in each table cell)
Reporting Entity [Axis]0000807882 (http://www.sec.gov/CIK)
Defined Benefit Plan Disclosure [Line Items]Period [Axis]
2015-09-28 - 2016-10-02
2014-09-29 - 2015-09-27
2013-09-30 - 2014-09-28
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis]Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis]Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Axis]
Qualified Pension Plan [Member]Supplemental Employee Retirement Plan [Member]Postretirement Health Plans [Member]Defined Benefit Plans and Other Postretirement Benefit Plans [Domain]Qualified Pension Plan [Member]Supplemental Employee Retirement Plan [Member]Postretirement Health Plans [Member]Qualified Pension Plan [Member]Supplemental Employee Retirement Plan [Member]Postretirement Health Plans [Member]
Assumptions used to determine benefit obligations, Discount rate
3.85% 1
3.60% 1
3.64% 1
 
4.79% 1
4.45% 1
4.47% 1
4.60% 1
4.36% 1
4.43% 1
Assumptions used to determine benefit obligations, Rate of future pay increases
0.00% 1
3.50% 1
  
3.50% 1
3.50% 1
 
3.50% 1
3.50% 1
 
Assumptions used to determine net periodic benefit cost, Discount rate
4.79% 2
4.45% 2
4.47% 2
 
4.60% 2
4.36% 2
4.43% 2
5.37% 2
4.88% 2
5.04% 2
Assumptions used to determine net periodic benefit cost, Long-term rate of return on assets
6.50% 2
   
6.50% 2
  
7.25% 2
  
Assumptions used to determine net periodic benefit cost, Rate of future pay increases
3.50% 2
3.50% 2
  
3.50% 2
3.50% 2
 
3.50% 2
3.50% 2
 
Cash flow period extension
   
P30Y  
      
1: Determined as of end of year
2: Determined as of beginning of year