Summary of Significant Accounting Policies - Revenue by Contract Type (Details)	3 Months Ended
	Mar. 27, 2020	Mar. 29, 2019
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	100.00%	100.00%
Time-and-material [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	82.40%	80.90%
Progress Billing [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	14.00%	10.70%
Percentage-of-completion [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	3.60%	8.40%