Segment Information (Revenues Earned Directly or Indirectly from the U.S. Federal Government and its Agencies) (Details)	12 Months Ended
Sep. 30, 2016	Oct. 02, 2015	Sep. 26, 2014
Segment Reporting [Abstract]
Percentage of revenue earned from the U.S. federal government and its agencies	21.40%	21.70%	17.80%

Percentage of revenue earned from the U.S. federal government and their agencies

No definition available.

Name:	jec_PercentageOfRevenueEarnedFromUSFederalGovernmentAndTheirAgencies
Namespace Prefix:	jec_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration