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Significant Accounting Policies (Basis to Determine Earned Relative TSR Restricted Stock Units) (Details) - Earned Relative TSR Restricted Stock Units	12 Months Ended
	Sep. 30, 2016
30th percentile
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
TSR Performance Multiplier	50.00%
50th percentile
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
TSR Performance Multiplier	100.00%
70th percentile or above
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
TSR Performance Multiplier	150.00%

X

- Definition

Share-based compensation arrangement by share-based payment award, equity instruments other than options, TSR performance multiplier.

+ References

No definition available.

+ Details

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Namespace Prefix:	jec_
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Balance Type:	na
Period Type:	duration

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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X

- Details

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Period Type:

X

- Details

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Namespace Prefix:
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Period Type:

X

- Details

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Namespace Prefix:
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X

- Details

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