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Restructuring and Other Charges - Summary of Restructuring and Other Charges Impacts on Reportable Segment Income by Line of Business (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jul. 02, 2021	Jun. 26, 2020	Jul. 02, 2021	Jun. 26, 2020
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 13,768	$ 19,681	$ 92,509	$ 112,309
Impairment of equity method investment			(40,138)	0
AWE Management Ltd
Restructuring Cost and Reserve [Line Items]
Impairment of equity method investment			(38,900)
CH2M HILL Companies, Ltd. \| Other Expense
Restructuring Cost and Reserve [Line Items]
Loss related to settlement				2,100
CH2M HILL Companies, Ltd. \| Continuing Operations \| Other Expense
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	8,000	19,700	53,600	109,600
CH2M HILL Companies, Ltd. \| Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	10,904	12,690	65,929	81,554
CH2M HILL Companies, Ltd. \| Critical Mission Solutions \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	921	3,173	4,840	11,248
CH2M HILL Companies, Ltd. \| People & Places Solutions \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	592	3,818	7,291	19,507
CH2M HILL Companies, Ltd. \| PA Consulting \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 1,351	$ 0	$ 14,449	$ 0