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
Jan. 01, 2021	Dec. 27, 2019
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 48,393
Impairment of equity method investment	(27,902)	$ 0
AWE Management Ltd
Restructuring Cost and Reserve [Line Items]
Impairment of equity method investment	(27,900)
CH2M HILL Companies, Ltd.
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	48,393	52,041
Loss related to settlement		2,400
CH2M HILL Companies, Ltd. \| Corporate
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	40,017	37,597
CH2M HILL Companies, Ltd. \| Critical Mission Solutions \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	3,209	4,291
CH2M HILL Companies, Ltd. \| People & Places Solutions \| Operating Segments
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	5,167	10,153
Other Expense \| CH2M HILL Companies, Ltd. \| Continuing Operations
Restructuring Cost and Reserve [Line Items]
Restructuring and other charges	$ 20,500	49,700
Other Expense \| CH2M HILL Companies, Ltd. \| Corporate \| United States
Restructuring Cost and Reserve [Line Items]
Loss related to settlement		$ (2,400)

This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

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Amount of gain (loss) recognized in settlement of litigation and insurance claims. Excludes claims within an insurance entity's normal claims settlement process.

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Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

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