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
	Jun. 26, 2020	Dec. 27, 2019	Jun. 28, 2019	Jun. 26, 2020	Jun. 28, 2019
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges				$ 112,309
CH2M HILL Companies, Ltd.
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 19,681		$ 95,959	112,309	$ 204,981
CH2M HILL Companies, Ltd. | Continuing Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	19,681		93,239	112,309	205,119
CH2M HILL Companies, Ltd. | Continuing Operations | Write-off of fixed assets
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			900		6,200
CH2M HILL Companies, Ltd. | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	12,690		74,921	81,554	127,986
CH2M HILL Companies, Ltd. | Critical Mission Solutions | Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	3,173		7,699	11,248	8,489
CH2M HILL Companies, Ltd. | People & Places Solutions | Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	3,818		10,619	19,507	68,644
CH2M HILL Companies, Ltd. | Energy, Chemicals and Resources (included in Discontinued Operations) | Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	0		2,720	0	(138)
Other Expense | CH2M HILL Companies, Ltd. | Continuing Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 19,700
Other Expense | CH2M HILL Companies, Ltd. | Corporate | United States
Restructuring Cost and Reserve [Line Items]
Gain (loss) related to settlement		$ 2,700	$ 0	$ (2,100)	$ 34,600