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
	Dec. 29, 2017	Dec. 30, 2016
Restructuring Cost And Reserve [Line Items]
Restructuring Charges	$ 19,349
CH2M HILL Companies, Ltd.
Restructuring Cost And Reserve [Line Items]
Restructuring Charges	19,349	$ 31,741
CH2M HILL Companies, Ltd. | Operating Segments | Aerospace & Technology
Restructuring Cost And Reserve [Line Items]
Restructuring Charges	289	170
CH2M HILL Companies, Ltd. | Operating Segments | Buildings & Infrastructure
Restructuring Cost And Reserve [Line Items]
Restructuring Charges	2,879	7,908
CH2M HILL Companies, Ltd. | Operating Segments | Industrial
Restructuring Cost And Reserve [Line Items]
Restructuring Charges	435	2,524
CH2M HILL Companies, Ltd. | Operating Segments | Petroleum & Chemicals
Restructuring Cost And Reserve [Line Items]
Restructuring Charges	3,363	13,584
CH2M HILL Companies, Ltd. | Corporate Non-Segment
Restructuring Cost And Reserve [Line Items]
Restructuring Charges	$ 12,383	$ 7,555