Revenue Recognition- Additional Information (Detail) - USD ($)	3 Months Ended
	Mar. 29, 2019	Mar. 30, 2018
Revenues	$ 99,031,000	$ 96,457,000
Deferred Revenue, Revenue Recognized	3,411,000
Subcontractor Fees Not Included In Revenues	4,200,000	10,200,000
Engineering and Other Scientific [Member] | Time And Materials Contracts [Member]
Revenues	65,379,000	64,557,000
Engineering and Other Scientific [Member] | Fixed Price Contracts [Member]
Revenues	14,875,000	12,446,000
Environmental and Health [Member] | Time And Materials Contracts [Member]
Revenues	18,018,000	18,614,000
Environmental and Health [Member] | Fixed Price Contracts [Member]
Revenues	759,000	840,000
Sales Revenue, Net [Member] | Time And Materials Contracts [Member]
Revenues	$ 83,397,000	$ 83,171,000
Concentration Risk, Percentage	84.00%	86.00%
Sales Revenue, Net [Member] | Fixed Price Contracts [Member]
Revenues	$ 15,634,000	$ 13,286,000
Concentration Risk, Percentage	16.00%	14.00%