Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Apr. 01, 2022	Apr. 02, 2021
Segment Reporting Information [Line Items]
Revenues	$ 128,478	$ 116,481
Operating Income	36,717	24,058
Capital Expenditures	2,795	2,306
Depreciation and Amortization	1,689	1,656
Operating segments
Segment Reporting Information [Line Items]
Operating Income	46,325	41,975
Capital Expenditures	614	653
Depreciation and Amortization	1,081	1,056
Corporate
Segment Reporting Information [Line Items]
Operating Income	(9,608)	(17,917)
Capital Expenditures	2,181	1,653
Depreciation and Amortization	608	600
Engineering and Other Scientific | Operating segments
Segment Reporting Information [Line Items]
Revenues	104,615	93,609
Operating Income	38,490	34,057
Capital Expenditures	564	604
Depreciation and Amortization	1,039	1,010
Environmental and Health | Operating segments
Segment Reporting Information [Line Items]
Revenues	23,863	22,872
Operating Income	7,835	7,918
Capital Expenditures	50	49
Depreciation and Amortization	$ 42	$ 46