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Description Of Business And Basis Of Presentation (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
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Sep. 30, 2011 | Oct. 01, 2010 | Oct. 02, 2009
Description Of Business And Basis Of Presentation |  |  |
Cost-reimbursable | 81.00% | 86.00% | 85.00%
Fixed-price | 16.00% | 13.00% | 14.00%
Guaranteed maximum price | 3.00% | 1.00% | 1.00%
Claim receivable write-off | $ 25.9 |  |

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- Definition Basis of Presentation + Details
Name: | jec_BasisOfPresentationAbstract
Namespace Prefix: | jec
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Claim Receivable Write Off + Details
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Namespace Prefix: | jec
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Revenue From Cost Reimbursable Contracts Percentage + Details
Name: | jec_RevenueFromCostReimbursableContractsPercentage
Namespace Prefix: | jec
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Revenue From Fixed Price Contracts Percentage + Details
Name: | jec_RevenueFromFixedPriceContractsPercentage
Namespace Prefix: | jec
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Definition Revenue From Guaranteed Maximum Price Contracts Percentage + Details
Name: | jec_RevenueFromGuaranteedMaximumPriceContractsPercentage
Namespace Prefix: | jec
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration