Revenue and Contract Balances - Disaggregation of Revenue (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jul. 02, 2023	Jul. 03, 2022	Jul. 02, 2023	Jul. 03, 2022
Disaggregation of Revenue [Line Items]
Revenue	$ 1,208,947	$ 890,231	$ 3,261,938	$ 2,601,485
Fixed-price
Disaggregation of Revenue [Line Items]
Revenue	452,605	335,014	1,194,266	982,565
Time-and-materials
Disaggregation of Revenue [Line Items]
Revenue	596,904	417,898	1,550,970	1,221,598
Cost-plus
Disaggregation of Revenue [Line Items]
Revenue	159,438	137,319	516,702	397,322
U.S. federal government
Disaggregation of Revenue [Line Items]
Revenue	338,022	261,434	996,471	781,503
U.S. state and local government
Disaggregation of Revenue [Line Items]
Revenue	151,462	150,731	452,447	465,770
U.S. commercial
Disaggregation of Revenue [Line Items]
Revenue	225,907	188,255	633,401	536,901
International
Disaggregation of Revenue [Line Items]
Revenue	$ 493,556	$ 289,811	$ 1,179,619	$ 817,311