Summary of Significant Accounting Policies - Revenue by Contract Type (Details)	3 Months Ended		6 Months Ended
	Jun. 29, 2018	Jun. 30, 2017	Jun. 29, 2018	Jun. 30, 2017
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	87.70%	85.60%	87.10%	85.60%
Progress Billing [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	9.80%	11.10%	9.90%	11.20%
Percentage-of-completion [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	2.50%	3.30%	3.00%	3.20%