Restructuring and Other Charges - Summary of Restructuring and Other Charges Impacts on Reportable Segment Income by Line of Business (Details) - USD ($) $ in Thousands	12 Months Ended
	Oct. 02, 2020	Sep. 27, 2019	Sep. 28, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 324,183
CH2M HILL Companies, Ltd.
Restructuring Cost and Reserve [Line Items]
Restructuring charges	324,183	$ 311,332	$ 190,806
CH2M HILL Companies, Ltd. | Continuing Operations
Restructuring Cost and Reserve [Line Items]
Restructuring charges	324,183	311,470	153,640
CH2M HILL Companies, Ltd. | Other Expense | Continuing Operations
Restructuring Cost and Reserve [Line Items]
Restructuring charges	321,600	337,000	154,000
Other miscellaneous adjustments	(500)	500	300
CH2M HILL Companies, Ltd. | Operating Segments | Critical Mission Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring charges	24,083	17,989	20,254
CH2M HILL Companies, Ltd. | Operating Segments | People & Places Solutions
Restructuring Cost and Reserve [Line Items]
Restructuring charges	170,631	108,835	56,238
CH2M HILL Companies, Ltd. | Operating Segments | Energy, Chemicals and Resources (included in Discontinued Operations)
Restructuring Cost and Reserve [Line Items]
Restructuring charges	0	(138)	37,166
CH2M HILL Companies, Ltd. | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 129,469	$ 184,646	$ 77,148