Revenue - Revenue by Contract Type (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2024	Sep. 29, 2023	Sep. 27, 2024	Sep. 29, 2023
Disaggregation of Revenue [Line Items]
Total revenue	$ 1,081,656	$ 1,001,507	$ 3,164,403	$ 2,922,819
Cost-plus and cost-reimbursable
Disaggregation of Revenue [Line Items]
Total revenue	$ 649,925	570,402	$ 1,850,584	1,589,619
Revenue, percent change	13.90%		16.40%
Firm-fixed-price
Disaggregation of Revenue [Line Items]
Total revenue	$ 403,132	402,219	$ 1,229,565	1,237,110
Revenue, percent change	0.20%		(0.60%)
Time-and-materials
Disaggregation of Revenue [Line Items]
Total revenue	$ 28,599	$ 28,886	$ 84,254	$ 96,090
Revenue, percent change	(1.00%)		(12.30%)