Revenue Recognition- Summary of Revenues (Detail) - Sales Revenue, Net [Member] - Revenue from Rights Concentration Risk [Member]	3 Months Ended		6 Months Ended
	Jul. 03, 2020	Jun. 28, 2019	Jul. 03, 2020	Jun. 28, 2019
Time And Materials Contracts [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	81.00%	85.00%	83.00%	85.00%
Time And Materials Contracts [Member] | Engineering and Other Scientific [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	60.00%	67.00%	63.00%	67.00%
Time And Materials Contracts [Member] | Environmental and Health [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	21.00%	18.00%	20.00%	18.00%
Fixed Price Contracts [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	19.00%	15.00%	17.00%	15.00%
Fixed Price Contracts [Member] | Engineering and Other Scientific [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	18.00%	14.00%	16.00%	14.00%
Fixed Price Contracts [Member] | Environmental and Health [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	1.00%	1.00%	1.00%	1.00%