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

No definition available.

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
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

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

- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ 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(19)(a))
-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 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(13))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: 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(a)(16)(a)(1))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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

- Definition

Weighted average interest rate of short-term debt outstanding calculated at point in time.

+ References

+ Details

Name:	us-gaap_ShortTermDebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_RevolvingCreditFacilityMember
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_DebtInstrumentAxis=jec_TermLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_VariableRateAxis=us-gaap_LondonInterbankOfferedRateLIBORMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_ShortTermDebtTypeAxis=jec_OtherLoanAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Borrowings - Term Loan Facility (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 28, 2018	Sep. 29, 2017
Eurocurrency Interest Rate \| Revolving Credit Facility \| Minimum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate	1.00%
Eurocurrency Interest Rate \| Revolving Credit Facility \| Maximum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate	1.50%
Eurocurrency Interest Rate \| Term Loan Facility \| Minimum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate	1.00%
Eurocurrency Interest Rate \| Term Loan Facility \| Maximum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate	1.50%
Base Interest Rate \| Revolving Credit Facility \| Minimum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate	0.00%
Base Interest Rate \| Revolving Credit Facility \| Maximum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate	50.00%
Base Interest Rate \| Term Loan Facility \| Minimum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate	0.00%
Base Interest Rate \| Term Loan Facility \| Maximum
Line of Credit Facility [Line Items]
Margin added to variable rate interest rate	0.50%
LIBOR \| Revolving Credit Facility \| Revolving Credit Facility \| Minimum \| Line of Credit
Line of Credit Facility [Line Items]
Stated interest rate	1.38%	1.00%
LIBOR \| Revolving Credit Facility \| Revolving Credit Facility \| Maximum \| Line of Credit
Line of Credit Facility [Line Items]
Stated interest rate	3.47%	2.23%
LIBOR \| Term Loan Facility
Line of Credit Facility [Line Items]
Stated interest rate	3.71%
Short-term credit agreements
Line of Credit Facility [Line Items]
Short-term debt	$ 5.0	$ 3.1
Weighted average interest rate	4.47%