Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2022	Jul. 02, 2021	Jul. 01, 2022	Jul. 02, 2021
Segment Reporting Information [Line Items]
Revenues	$ 130,281	$ 119,877	$ 258,759	$ 236,358
Operating Income	45,277	29,372	81,994	53,430
Capital Expenditures	4,656	1,499	7,451	3,805
Depreciation and Amortization	1,812	1,642	3,501	3,298
Operating segments
Segment Reporting Information [Line Items]
Operating Income	46,878	45,409	93,203	87,384
Capital Expenditures	1,622	844	2,236	1,497
Depreciation and Amortization	1,195	1,023	2,276	2,079
Corporate
Segment Reporting Information [Line Items]
Operating Income	(1,601)	(16,037)	(11,209)	(33,954)
Capital Expenditures	3,034	655	5,215	2,308
Depreciation and Amortization	617	619	1,225	1,219
Engineering and Other Scientific | Operating segments
Segment Reporting Information [Line Items]
Revenues	109,150	98,139	213,765	191,748
Operating Income	40,032	37,914	78,522	71,970
Capital Expenditures	1,616	814	2,180	1,418
Depreciation and Amortization	1,154	976	2,193	1,986
Environmental and Health | Operating segments
Segment Reporting Information [Line Items]
Revenues	21,131	21,738	44,994	44,610
Operating Income	6,846	7,495	14,681	15,414
Capital Expenditures	6	30	56	79
Depreciation and Amortization	$ 41	$ 47	$ 83	$ 93