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		6 Months Ended
	Mar. 27, 2020	Mar. 29, 2019	Mar. 27, 2020	Mar. 29, 2019
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges			$ 92,627
CH2M HILL Companies, Ltd.
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 40,586	$ 69,622	92,627	$ 109,023
CH2M HILL Companies, Ltd. | Continuing Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	40,586	66,821	92,627	111,880
CH2M HILL Companies, Ltd. | Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	31,265	18,854	68,862	53,065
CH2M HILL Companies, Ltd. | Critical Mission Solutions | Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	3,785	341	8,076	790
CH2M HILL Companies, Ltd. | People & Places Solutions | Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	5,536	47,626	15,689	58,025
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	2,801	0	(2,857)
Other Expense | CH2M HILL Companies, Ltd. | Continuing Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges		93,900		$ 141,200
Other Expense | CH2M HILL Companies, Ltd. | Corporate
Restructuring Cost and Reserve [Line Items]
Gain (loss) related to settlement		$ 32,400	$ (2,100)