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Savings and Deferred Compensation Plans (Deferred Compensation Plans) (Details) - USD ($) $ in Thousands | 12 Months Ended
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Sep. 29, 2017 | Sep. 30, 2016 | Oct. 02, 2015
Savings And Deferred Compensation Plans [Abstract] |  |  |
Deferred compensation plans expense | $ 4,368 | $ 5,792 | $ 5,536

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- Definition Savings and deferred compensation plans. + References No definition available. + Details
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Namespace Prefix: | jec_
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Balance Type: | na
Period Type: | duration

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- Definition The compensation expense recognized during the period pertaining to the deferred compensation arrangement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 710 -SubTopic 10 -Section 30 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6409875&loc=d3e20015-108363 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | debit
Period Type: | duration