Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Apr. 02, 2021	Apr. 03, 2020
Segment Reporting Information [Line Items]
Revenues	$ 116,481	$ 105,953
Operating Income	24,058	35,988
Capital Expenditures	2,306	1,039
Depreciation and Amortization	1,656	1,786
Operating segments
Segment Reporting Information [Line Items]
Operating Income	41,975	33,894
Capital Expenditures	653	628
Depreciation and Amortization	1,056	1,184
Corporate
Segment Reporting Information [Line Items]
Operating Income	(17,917)	2,094
Capital Expenditures	1,653	411
Depreciation and Amortization	600	602
Engineering and Other Scientific | Operating segments
Segment Reporting Information [Line Items]
Revenues	93,609	84,887
Operating Income	34,057	26,641
Capital Expenditures	604	566
Depreciation and Amortization	1,010	1,137
Environmental and Health | Operating segments
Segment Reporting Information [Line Items]
Revenues	22,872	21,066
Operating Income	7,918	7,253
Capital Expenditures	49	62
Depreciation and Amortization	$ 46	$ 47