Equipment financing noncurrent.

No definition available.

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

- Definition

Line of credit facility maturity period.

+ References

No definition available.

+ Details

Name:	jec_LineOfCreditFacilityMaturityPeriod
Namespace Prefix:	jec_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

- 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
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e845-128460

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e848-128460

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

+ Details

Name:	us-gaap_BusinessAcquisitionEffectiveDateOfAcquisition1
Namespace Prefix:	us-gaap_
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

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ 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

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ 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

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

- Details

Name:	us-gaap_CreditFacilityAxis=jec_EurocurrencyInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=jec_BaseInterestRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=jec_CH2MHILLCompaniesLimitedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=jec_EquipmentFinancingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=jec_TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Long-term Debt (Term Loan Facility) (Narrative) (Details) - USD ($) $ in Thousands		3 Months Ended
	Dec. 15, 2017	Dec. 29, 2017	Sep. 28, 2017
Line of Credit Facility [Line Items]
Equipment financing		$ 6,553
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		$ 6,600
CH2M HILL Companies, Ltd. \| Equipment Financing
Line of Credit Facility [Line Items]
Line of credit facility, maturity period		2021-09
Payment due in installments		Monthly
CH2M HILL Companies, Ltd. \| Minimum \| Equipment Financing
Line of Credit Facility [Line Items]
Interest rates at equipment financing		0.22%
CH2M HILL Companies, Ltd. \| Maximum \| Equipment Financing
Line of Credit Facility [Line Items]
Interest rates at equipment financing		3.29%
Term Loan Facility
Line of Credit Facility [Line Items]
Direct borrowings on credit facility		$ 1,500,000	$ 1,500,000
Line of credit facility, maturity period		2020-12
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