Revenue Recognition- Summary of Percent of Revenues (Detail) - Revenue from Rights Concentration Risk	12 Months Ended
	Jan. 03, 2020	Dec. 28, 2018
Engineering and Other Scientific [Member] | Time And Materials Contracts [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	66.00%	64.00%
Engineering and Other Scientific [Member] | Fixed Price Contracts [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	15.00%	17.00%
Environmental and Health [Member] | Time And Materials Contracts [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	18.00%	18.00%
Environmental and Health [Member] | Fixed Price Contracts [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	1.00%	1.00%
Sales Revenue, Net [Member] | Time And Materials Contracts [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	84.00%	82.00%
Sales Revenue, Net [Member] | Fixed Price Contracts [Member]
Disaggregation Of Revenue [Line Items]
Concentration Risk, Percentage	16.00%	18.00%