Summary of Significant Accounting Policies - Revenue by Contract Type (Details)	3 Months Ended
	Mar. 30, 2018	Mar. 31, 2017
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	86.30%	85.60%
Progress Billing [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	10.10%	11.30%
Percentage-of-completion [Member]
Schedule Of Revenue By Contract Type [Line Items]
Revenue percent	3.60%	3.10%