Earnings Per Share and Certain Related Information - Schedule of Compute Basic and Diluted of EPS (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 26, 2025	Sep. 27, 2024	Sep. 29, 2023
Numerator for Basic and Diluted EPS:
Net earnings attributable to Jacobs from continuing operations	$ 313,302	$ 612,804	$ 379,125
Redeemable Noncontrolling interests redemption value adjustment (See Note 15- PA Consulting Redeemable Noncontrolling Interests)	912	(10,274)	8,340
Net earnings from continuing operations allocated to common stock for EPS calculation	314,214	602,530	387,465
Net (loss) earnings from discontinued operations allocated to common stock for EPS calculation	(23,966)	193,289	286,652
Net earnings allocated to common stock for EPS calculation	$ 290,248	$ 795,819	$ 674,117
Denominator for Basic and Diluted EPS:
Shares used for calculating basic EPS attributable to common stock (in shares)	121,468	125,324	126,607
Effect of dilutive securities:
Stock compensation plans (in shares)	464	557	607
Shares used for calculating diluted EPS attributable to common stock (in shares)	121,932	125,881	127,214
Net Earnings Per Share:
Basic Net Earnings from Continuing Operations Per Share (in dollars per share)	$ 2.59	$ 4.81	$ 3.06
Basic Net Earnings from Discontinued Operations Per Share (in dollars per share)	(0.20)	1.54	2.26
Basic Earnings Per Share (in dollars per share)	2.39	6.35	5.32
Diluted Earnings Per Share:
Diluted Net Earnings from Continuing Operations Per Share (in dollars per share)	2.58	4.79	3.05
Diluted Net Earnings from Discontinued Operations Per Share (in dollars per share)	(0.20)	1.54	2.25
Diluted Earnings Per Share (in dollars per share)	$ 2.38	$ 6.32	$ 5.30