Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 03, 2020	Jun. 28, 2019	Jul. 03, 2020	Jun. 28, 2019
Segment Reporting Information [Line Items]
Revenues	$ 92,045	$ 106,506	$ 197,998	$ 205,537
Operating Income	9,120	24,823	45,108	40,577
Capital Expenditures	1,644	6,900	2,683	13,241
Depreciation and Amortization	1,701	1,642	3,487	3,232
Operating segments
Segment Reporting Information [Line Items]
Operating Income	27,856	36,291	61,750	68,461
Capital Expenditures	920	942	1,548	2,763
Depreciation and Amortization	1,114	1,218	2,298	2,384
Corporate
Segment Reporting Information [Line Items]
Operating Income	(18,736)	(11,468)	(16,642)	(27,884)
Capital Expenditures	724	5,958	1,135	10,478
Depreciation and Amortization	587	424	1,189	848
Engineering and Other Scientific | Operating segments
Segment Reporting Information [Line Items]
Revenues	72,123	86,820	157,009	167,074
Operating Income	20,807	29,252	47,448	55,226
Capital Expenditures	901	929	1,467	2,707
Depreciation and Amortization	1,068	1,170	2,205	2,291
Environmental and Health | Operating segments
Segment Reporting Information [Line Items]
Revenues	19,922	19,686	40,989	38,463
Operating Income	7,049	7,039	14,302	13,235
Capital Expenditures	19	13	81	56
Depreciation and Amortization	$ 46	$ 48	$ 93	$ 93