Consolidated Statement of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Total Jacobs Stockholders’ Equity	Noncontrolling Interests
Beginning balance at Sep. 28, 2018	$ 5,944,354	$ 142,218	$ 2,708,839	$ 3,809,991	$ (806,703)	$ 5,854,345	$ 90,009
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	192,363			181,213		181,213	11,150
Foreign currency translation adjustment	(21,048)
Foreign currency translation adjustments, net of deferred taxes	(21,048)				(21,048)	(21,048)
Pension and retiree medical plan liability, net of deferred taxes	(34,114)				(34,114)	(34,114)
Gain on derivative, net of deferred taxes	1,605				1,605	1,605
Dividends	(23,929)			(23,929)		(23,929)
Noncontrolling interests - distributions and other	(11,432)						(11,432)
Stock based compensation	28,916		28,910	6		28,916
Noncontrolling interest acquired / consolidated	(1,113)		(1,113)			(1,113)
Issuances of equity securities including shares withheld for taxes	5,623	913	9,854	(5,144)		5,623
Repurchases of equity securities	(488,435)	(6,699)	(177,681)	(304,055)		(488,435)
Ending balance at Mar. 29, 2019	5,555,581	136,432	2,568,809	3,620,873	(860,260)	5,465,854	89,727
Beginning balance at Dec. 28, 2018	5,841,034	140,400	2,672,390	3,796,864	(856,552)	5,753,102	87,932
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	62,773			56,917		56,917	5,856
Foreign currency translation adjustment	31,352					31,352
Pension and retiree medical plan liability, net of deferred taxes	(35,418)				(35,418)	(35,418)
Gain on derivative, net of deferred taxes	358				358	358
Dividends	(23,696)			(23,696)		(23,696)
Noncontrolling interests - distributions and other	(4,061)						(4,061)
Stock based compensation	13,322		13,322			13,322
Issuances of equity securities including shares withheld for taxes	16,553	407	16,362	(216)		16,553
Repurchases of equity securities	(346,636)	(4,375)	(133,265)	(208,996)		(346,636)
Ending balance at Mar. 29, 2019	5,555,581	136,432	2,568,809	3,620,873	(860,260)	5,465,854	89,727
Beginning balance at Sep. 27, 2019	5,768,658	132,879	2,559,450	3,939,174	(916,812)	5,714,691	53,967
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	177,466			164,926		164,926	12,540
Foreign currency translation adjustment	(64,278)
Foreign currency translation adjustments, net of deferred taxes	(45,849)				(45,849)	(45,849)
Pension and retiree medical plan liability, net of deferred taxes	16,326				16,326	16,326
Gain on derivative, net of deferred taxes	18				18	18
Dividends	(25,522)			(25,522)		(25,522)
Noncontrolling interests - distributions and other	(10,305)		5,002			5,002	(15,307)
Stock based compensation	23,835		22,733	1,102		23,835
Issuances of equity securities including shares withheld for taxes	(5,822)	682	2,179	(8,683)		(5,822)
Repurchases of equity securities	(285,822)	(3,576)	(19,947)	(262,299)		(285,822)
Ending balance at Mar. 27, 2020	5,612,983	129,985	2,569,417	3,808,698	(946,317)	5,561,783	51,200
Beginning balance at Dec. 27, 2019	6,062,171	133,001	2,605,765	4,145,825	(880,166)	6,004,425	57,746
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings (loss)	(85,803)			(92,087)		(92,087)	6,284
Foreign currency translation adjustment	(116,575)
Foreign currency translation adjustments, net of deferred taxes	(98,146)				(98,146)	(98,146)
Pension and retiree medical plan liability, net of deferred taxes	31,995				31,995	31,995
Dividends	(25,453)			(25,453)		(25,453)
Noncontrolling interests - distributions and other	(7,828)		5,002			5,002	(12,830)
Stock based compensation	9,557		9,533	24		9,557
Issuances of equity securities including shares withheld for taxes	12,312	208	12,294	(190)		12,312
Repurchases of equity securities	(285,822)	(3,224)	(63,177)	(219,421)		(285,822)
Ending balance at Mar. 27, 2020	$ 5,612,983	$ 129,985	$ 2,569,417	$ 3,808,698	$ (946,317)	$ 5,561,783	$ 51,200