Share-based compensation arrangement by share-based payment award, award number of shares, fungible share basis.

No definition available.

Name:	jec_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardNumberOfSharesFungibleShareBasis
Namespace Prefix:	jec_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Share-based compensation arrangement by share-based payment award, award number of shares, non-fungible share basis.

+ References

No definition available.

+ Details

Name:	jec_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardNumberOfSharesNonFungibleShareBasis
Namespace Prefix:	jec_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(i)-(ii)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

Name:	us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
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_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_PlanNameAxis=jec_NineteenNinetyNineStockIncentivePlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_RestrictedStockUnitsRSUMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=jec_RestrictedStockNonFungibleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=jec_RestrictedStockFungibleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=jec_ServiceConditionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=jec_RestrictedStockUnitsNonFungibleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AwardTypeAxis=jec_RestrictedStockUnitsFungibleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_VestingAxis=jec_ServiceMarketAndPerformanceConditionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PlanNameAxis=jec_NineteenNinetyNineOutsideDirectorStockPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Employee Stock Purchase and Stock Option Plans (Number of Shares of Restricted Stock and Restricted Stock Units Issued Under the 1999 Plans) (Details) - shares	12 Months Ended
	Sep. 30, 2016	Oct. 02, 2015	Sep. 26, 2014
Stock Option Plans 1999 SIP \| Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units issued	597,091	507,882	589,150
Award number of shares, non-fungible share basis (in shares)	1
Restricted stock and restricted stock units cancelled	512,903	326,480	147,221
Award number of shares, fungible share basis (in shares)	1.92
Restricted stock and restricted stock units outstanding	1,690,077
Stock Option Plans 1999 SIP \| Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award number of shares, non-fungible share basis (in shares)	1
Award number of shares, fungible share basis (in shares)	1.92
Stock Option Plans 1999 SIP \| Restricted stock, non fungible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units outstanding	245,150
Stock Option Plans 1999 SIP \| Restricted stock, fungible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units outstanding	1,444,927
Stock Option Plans 1999 SIP \| Service Condition \| Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units issued	183,131	126,635	287,545
Restricted stock and restricted stock units cancelled	177,640	70,296	12,333
Restricted stock and restricted stock units outstanding	523,888
Stock Option Plans 1999 SIP \| Service Condition \| Restricted stock units, non fungible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units outstanding	57,300
Stock Option Plans 1999 SIP \| Service Condition \| Restricted stock units, fungible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units outstanding	466,588
Stock Option Plans 1999 SIP \| Service, Market, And Performance Conditions \| Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units issued	372,794	219,965	432,700
Restricted stock and restricted stock units cancelled	275,933	194,116	52,000
Restricted stock and restricted stock units outstanding	721,934
Stock Option Plans 1999 SIP \| Service, Market, And Performance Conditions \| Restricted stock units, non fungible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units outstanding	0
Stock Option Plans 1999 SIP \| Service, Market, And Performance Conditions \| Restricted stock units, fungible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units outstanding	721,934
Stock Option Plans 1999 ODSP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award number of shares, non-fungible share basis (in shares)	1
Stock Option Plans 1999 ODSP \| Restricted stock, non fungible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units outstanding	34,000
Stock Option Plans 1999 ODSP \| Service Condition
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units issued	23,090	13,500	15,000
Stock Option Plans 1999 ODSP \| Service Condition \| Restricted stock units, non fungible
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock and restricted stock units outstanding	88,590