Summary of Significant Accounting Policies - Revenue by Contract Type (Details)	3 Months Ended		6 Months Ended
	Jun. 26, 2020	Jun. 28, 2019	Jun. 26, 2020	Jun. 28, 2019
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	100.00%	100.00%	100.00%	100.00%
Time-and-material [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	78.90%	79.30%	80.50%	79.70%
Progress Billing [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	16.20%	10.40%	15.10%	10.60%
Percentage-of-completion [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	4.90%	10.30%	4.40%	9.70%