Segment Information - Schedule of Total Revenues, Segment Operating Profit and Total Asset for Reporting Segment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 29, 2018	Jun. 30, 2017	Jun. 29, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenues from External Customers	$ 4,156,663	$ 2,514,751	$ 10,842,001	$ 7,368,922
Total Segment Operating Profit	212,729	128,475	406,659	285,276
Restructuring and Other Charges	(46,922)	(10,700)	(135,156)	(114,666)
Total Other (Expense) Income, net	(19,946)	(1,079)	(49,792)	(11,509)
Earnings Before Taxes	192,783	127,396	356,867	273,767
Restructuring charges excluded segment profit			135,156
CH2M HILL Companies, Ltd.
Segment Reporting Information [Line Items]
CH2M Transaction Costs	(4,422)	0	(76,915)	0
Restructuring charges excluded segment profit	46,456	10,700	135,156	115,899
CH2M HILL Companies, Ltd. | Other Expense
Segment Reporting Information [Line Items]
Restructuring and Other Charges				(1,200)
Amortization of deferred financing fees	500		1,200
Operating Segments
Segment Reporting Information [Line Items]
Total Segment Operating Profit	297,204	168,166	729,649	455,567
Corporate (1)
Segment Reporting Information [Line Items]
Other Corporate Expenses (3)	(33,131)	(28,991)	(110,919)	(55,625)
Other corporate charges associated with a certain project	(15,000)
Corporate (1) | CH2M HILL Companies, Ltd.
Segment Reporting Information [Line Items]
Restructuring charges excluded segment profit	(19,282)	2,866	50,486	30,784
Aerospace, Technology, Environmental and Nuclear
Segment Reporting Information [Line Items]
Revenues from External Customers	1,221,306	610,643	3,072,900	1,815,871
Aerospace, Technology, Environmental and Nuclear | Operating Segments
Segment Reporting Information [Line Items]
Revenues from External Customers	1,221,306	610,643	3,072,900	1,815,871
Total Segment Operating Profit	89,334	49,383	217,003	143,781
Litigation expenses included in segment profit	15,000		15,000
Aerospace, Technology, Environmental and Nuclear | Operating Segments | CH2M HILL Companies, Ltd.
Segment Reporting Information [Line Items]
Restructuring charges excluded segment profit	16,936	(18)	18,655	1,628
Buildings, Infrastructure and Advanced Facilities
Segment Reporting Information [Line Items]
Revenues from External Customers	1,707,072	987,159	4,497,249	2,823,882
Buildings, Infrastructure and Advanced Facilities | Operating Segments
Segment Reporting Information [Line Items]
Revenues from External Customers	1,707,072	987,159	4,497,249	2,823,882
Total Segment Operating Profit	145,901	72,991	347,887	191,680
Restructuring charges excluded segment profit	22,600		22,600
Buildings, Infrastructure and Advanced Facilities | Operating Segments | CH2M HILL Companies, Ltd.
Segment Reporting Information [Line Items]
Restructuring charges excluded segment profit	32,423	8,504	53,603	47,697
Energy, Chemicals and Resources
Segment Reporting Information [Line Items]
Revenues from External Customers	1,228,285	916,949	3,271,852	2,729,169
Energy, Chemicals and Resources | Operating Segments
Segment Reporting Information [Line Items]
Revenues from External Customers	1,228,285	916,949	3,271,852	2,729,169
Total Segment Operating Profit	61,969	45,792	164,759	120,106
Energy, Chemicals and Resources | Operating Segments | CH2M HILL Companies, Ltd.
Segment Reporting Information [Line Items]
Restructuring charges excluded segment profit	$ 16,379	$ (652)	$ 12,412	$ 35,790