Summary of Significant Accounting Policies - Revenue by Contract Type (Details)	3 Months Ended
	Mar. 29, 2019	Mar. 30, 2018
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	80.90%	86.30%
Progress Billing [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	10.70%	10.10%
Percentage-of-completion [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	8.40%	3.60%