Restructuring and Other Charges - Summary of Restructuring and Other Activities by Major Type of Costs (Details) - CH2M HILL Companies, Ltd. - 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 costs	$ 40,586	$ 66,821	$ 92,627	$ 111,880
Lease Abandonments
Restructuring Cost and Reserve [Line Items]
Restructuring costs	4,782	40,323	4,782	49,314
Involuntary Terminations
Restructuring Cost and Reserve [Line Items]
Restructuring costs	4,925	7,851	18,078	10,760
Outside Services
Restructuring Cost and Reserve [Line Items]
Restructuring costs	23,405	37,705	54,871	55,903
Other
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 7,474	$ (19,058)	$ 14,896	$ (4,097)