Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Jan. 01, 2016	Oct. 02, 2015	Jul. 03, 2015	Apr. 03, 2015	Jan. 02, 2015	Oct. 03, 2014	Jul. 04, 2014	Apr. 04, 2014	Jan. 01, 2016		Jan. 02, 2015		Jan. 03, 2014
Segment Reporting Information [Line Items]
Revenues	$ 73,681	$ 78,994	$ 79,864	$ 80,293	$ 73,611	$ 78,557	$ 76,574	$ 75,962	$ 312,832	[1]	$ 304,704	[1]	$ 296,168	[1]
Operating Income	$ 14,279	$ 20,921	$ 18,705	$ 15,028	$ 14,133	$ 19,238	$ 16,084	$ 14,094	68,933		63,549		55,946
Capital Expenditures									5,379		4,947		6,226
Depreciation and Amortization									5,479		5,404		4,951
Engineering and Other Scientific
Segment Reporting Information [Line Items]
Revenues									237,959		223,384		215,972
Operating Income									76,817		72,207		67,070
Capital Expenditures									3,197		3,719		5,180
Depreciation and Amortization									3,919		3,637		3,097
Environmental and Health
Segment Reporting Information [Line Items]
Revenues									74,873		81,320		80,196
Operating Income									21,810		25,145		25,072
Capital Expenditures									164		211		148
Depreciation and Amortization									182		197		299
Operating segments
Segment Reporting Information [Line Items]
Operating Income									98,627		97,352		92,142
Capital Expenditures									3,361		3,930		5,328
Depreciation and Amortization									4,101		3,834		3,396
Corporate
Segment Reporting Information [Line Items]
Operating Income									(29,694)		(33,803)		(36,196)
Capital Expenditures									2,018		1,017		898
Depreciation and Amortization									$ 1,378		$ 1,570		$ 1,555

[1] Geographic revenues are allocated based on the location of the client.