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. 29, 2017	$ 4,487,351	$ 120,386	$ 1,239,782	$ 3,721,698	$ (653,514)	$ 4,428,352	$ 58,999
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	54,493			50,750		50,750	3,743
Foreign currency translation adjustments	27,694					27,694
Pension and retiree medical plan liability, net of deferred taxes	7,844				7,844	7,844
Gain on derivatives, net of deferred taxes	912				912	912
Noncontrolling interest acquired / consolidated	38,193						38,193
Dividends	(21,384)			(21,384)		(21,384)
Distributions to noncontrolling interests	(4,321)			7,705		7,705	(12,026)
Stock based compensation	47,189		49,043	(1,854)		47,189
Issuances of equity securities including shares withheld for taxes	1,390,456	21,378	1,370,373	(1,295)		1,390,456
Repurchases of equity securities	(2,951)	(49)	(2,933)	31		2,951
Ending balance at Mar. 30, 2018	6,025,476	141,715	2,656,265	3,755,651	(617,064)	5,936,567	88,909
Beginning balance at Dec. 29, 2017	5,961,747	141,557	2,628,012	3,728,527	(628,985)	5,869,111	92,636
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net earnings	51,932			48,587		48,587	3,345
Foreign currency translation adjustments	9,714					9,714
Pension and retiree medical plan liability, net of deferred taxes	2,177				2,177	2,177
Gain on derivatives, net of deferred taxes	30				30	30
Noncontrolling interest acquired / consolidated	(2,773)						(2,773)
Dividends	(21,384)			(21,384)		(21,384)
Distributions to noncontrolling interests	(4,299)			0		0	(4,299)
Stock based compensation	22,570		22,570			22,570
Issuances of equity securities including shares withheld for taxes	8,713	207	8,616	(110)		8,713
Repurchases of equity securities	(2,951)	(49)	(2,933)	31		(2,951)
Ending balance at Mar. 30, 2018	6,025,476	141,715	2,656,265	3,755,651	(617,064)	5,936,567	88,909
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Adoption of ASC 606, net of deferred taxes of ($10,285) | Accounting Standards Update 2014-09	(37,209)			(37,209)		(37,209)
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	192,363			181,213		181,213	5,856
Foreign currency translation adjustments	(21,048)					(21,048)
Pension and retiree medical plan liability, net of deferred taxes	(34,114)				(34,114)	(34,114)
Gain on derivatives, net of deferred taxes	1,605				1,605	1,605
Noncontrolling interest acquired / consolidated	(1,113)		(1,113)			(1,113)
Dividends	(23,929)			(23,929)		(23,929)
Distributions to noncontrolling interests	(11,432)						(11,432)
Stock based compensation	28,916		28,910	6		28,916
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	62,773			56,917		56,917	11,150
Foreign currency translation adjustments	31,352					31,352
Pension and retiree medical plan liability, net of deferred taxes	(35,418)				(35,418)	(35,418)
Gain on derivatives, net of deferred taxes	358				358	358
Dividends	(23,696)			(23,696)		(23,696)
Distributions to noncontrolling interests	(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