Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jul. 01, 2022	Jun. 30, 2023	Jul. 01, 2022
Segment Reporting Information [Line Items]
Revenues	$ 140,221	$ 130,281	$ 280,530	$ 258,759
Operating Income	29,875	45,277	58,995	81,994
Capital Expenditures	9,567	4,656	15,428	7,451
Depreciation and Amortization	2,186	1,812	4,174	3,501
Operating segments
Segment Reporting Information [Line Items]
Operating Income	46,232	46,878	97,405	93,203
Capital Expenditures	1,280	1,622	2,783	2,236
Depreciation and Amortization	1,426	1,195	2,780	2,276
Corporate
Segment Reporting Information [Line Items]
Operating Income	(16,357)	(1,601)	(38,410)	(11,209)
Capital Expenditures	8,287	3,034	12,645	5,215
Depreciation and Amortization	760	617	1,394	1,225
Engineering and Other Scientific | Operating segments
Segment Reporting Information [Line Items]
Revenues	116,647	109,150	233,695	213,765
Operating Income	38,711	40,032	82,330	78,522
Capital Expenditures	1,261	1,616	2,669	2,180
Depreciation and Amortization	1,372	1,154	2,678	2,193
Environmental and Health | Operating segments
Segment Reporting Information [Line Items]
Revenues	23,574	21,131	46,835	44,994
Operating Income	7,521	6,846	15,075	14,681
Capital Expenditures	19	6	114	56
Depreciation and Amortization	$ 54	$ 41	$ 102	$ 83