Debt Instrument, Contingent Interest Rate, Increase (Decrease)

No definition available.

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Namespace Prefix:	jec_
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Period Type:	instant

- Definition

Equipment financing noncurrent.

+ References

No definition available.

+ Details

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Namespace Prefix:	jec_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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Data Type:	xbrli:dateItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Description of the frequency of periodic payments (monthly, quarterly, annual).

+ References

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+ Details

Name:	us-gaap_DebtInstrumentFrequencyOfPeriodicPayment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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+ Details

Name:	us-gaap_LineOfCredit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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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Balance Type:	na
Period Type:	duration

- Details

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Balance Type:
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- Details

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Balance Type:
Period Type:

- Details

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- Details

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- Details

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- Details

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- Details

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Balance Type:
Period Type:

- Details

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- Details

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- Details

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Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=jec_SeniorNotesSeriesCDueMay2030Member
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Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
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Period Type:

Long-term Debt - Term Loan Facility (Narrative) (Details) - USD ($)		6 Months Ended
	Dec. 15, 2017	Mar. 30, 2018	Mar. 12, 2018	Sep. 29, 2017	Sep. 28, 2017
Senior Notes
Line of Credit Facility [Line Items]
Debt Instrument, Contingent Interest Rate, Increase (Decrease)		0.75%
Aggregate principal amount			$ 500,000,000
Eurocurrency Interest Rate \| Minimum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)		1.00%
Eurocurrency Interest Rate \| Maximum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)		1.50%
Base Interest Rate \| Minimum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)		0.00%
Base Interest Rate \| Maximum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)		0.50%
CH2M HILL Companies, Ltd.
Line of Credit Facility [Line Items]
Acquisition date	Dec. 15, 2017
Equipment financing		$ 5,900,000
CH2M HILL Companies, Ltd. \| Senior Notes
Line of Credit Facility [Line Items]
Equipment financing		2,500,000
CH2M HILL Companies, Ltd. \| Equipment Financing
Line of Credit Facility [Line Items]
Equipment financing		$ 3,400,000
Payment due in installments		monthly
CH2M HILL Companies, Ltd. \| Minimum \| Equipment Financing
Line of Credit Facility [Line Items]
Stated interest rate		0.22%
CH2M HILL Companies, Ltd. \| Maximum \| Equipment Financing
Line of Credit Facility [Line Items]
Stated interest rate		3.29%
Term Loan Facility
Line of Credit Facility [Line Items]
Direct borrowings on credit facility		$ 1,500,000,000		$ 0	$ 1,500,000,000
Term Loan Facility \| Eurocurrency Interest Rate \| Minimum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)		1.00%
Term Loan Facility \| Eurocurrency Interest Rate \| Maximum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)		1.50%
Term Loan Facility \| Base Interest Rate \| Minimum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)		0.00%
Term Loan Facility \| Base Interest Rate \| Maximum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)		0.50%
Term Loan Facility \| CH2M HILL Companies, Ltd.
Line of Credit Facility [Line Items]
Acquisition date		Dec. 15, 2017
Senior Notes, Series A \| Senior Notes
Line of Credit Facility [Line Items]
Aggregate principal amount			$ 190,000,000
Stated interest rate			4.27%
Senior Notes, Series B \| Senior Notes
Line of Credit Facility [Line Items]
Aggregate principal amount			$ 180,000,000
Stated interest rate			4.42%
Senior Notes, Series C \| Senior Notes
Line of Credit Facility [Line Items]
Aggregate principal amount			$ 130,000,000
Stated interest rate			4.52%
LIBOR \| CH2M HILL Companies, Ltd. \| Senior Notes
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate (percentage)		2.50%