v3.26.1
Restructuring and Other Charges - Schedule of Restructuring and Other Activities by Major Type of Costs (Details) - CH2M Hill, KeyM, John Wood Group Acquisitions and ECR Sale - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Mar. 27, 2026
Mar. 28, 2025
Mar. 27, 2026
Mar. 28, 2025
Restructuring Cost and Reserve [Line Items]        
Restructuring costs $ 14,171 $ 10,663 $ 18,169 $ 25,403
Voluntary and Involuntary Termination        
Restructuring Cost and Reserve [Line Items]        
Restructuring costs 8,056 4,503 9,765 4,888
Outside Services        
Restructuring Cost and Reserve [Line Items]        
Restructuring costs 1,865 4,956 3,040 16,368
Other        
Restructuring Cost and Reserve [Line Items]        
Restructuring costs 4,250 $ 1,204 5,364 $ 4,147
Professional Services Related to PA Consulting Transaction        
Restructuring Cost and Reserve [Line Items]        
Restructuring costs $ 2,200   $ 2,500