Savings and Deferred Compensation Plans - Schedule of Savings Plans Contributions (Details) - USD ($) $ in Thousands	12 Months Ended
Sep. 26, 2025	Sep. 27, 2024	Sep. 29, 2023
Savings And Deferred Compensation Plans [Abstract]
Savings plans contributions	$ 169,610	$ 169,727	$ 147,288

Defined Contribution Plan Savings Plans Contributions

No definition available.

Name:	jec_DefinedContributionPlanSavingsPlansContributions
Namespace Prefix:	jec_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration