Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 28, 2024	Jun. 30, 2023	Jun. 28, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Revenues	$ 140,536	$ 140,221	$ 285,469	$ 280,530
Operating Income	35,744	29,875	66,457	58,995
Capital Expenditures	1,007	9,567	2,516	15,428
Depreciation and Amortization	2,486	2,186	4,810	4,174
Operating segments
Segment Reporting Information [Line Items]
Operating Income	51,024	46,232	107,891	97,405
Capital Expenditures	510	1,280	956	2,783
Depreciation and Amortization	1,819	1,426	3,496	2,780
Corporate
Segment Reporting Information [Line Items]
Operating Income	(15,280)	(16,357)	(41,434)	(38,410)
Capital Expenditures	497	8,287	1,560	12,645
Depreciation and Amortization	667	760	1,314	1,394
Engineering and Other Scientific | Operating segments
Segment Reporting Information [Line Items]
Revenues	118,477	116,647	239,948	233,695
Operating Income	43,765	38,711	92,396	82,330
Capital Expenditures	465	1,261	882	2,669
Depreciation and Amortization	1,765	1,372	3,393	2,678
Environmental and Health | Operating segments
Segment Reporting Information [Line Items]
Revenues	22,059	23,574	45,521	46,835
Operating Income	7,259	7,521	15,495	15,075
Capital Expenditures	45	19	74	114
Depreciation and Amortization	$ 54	$ 54	$ 103	$ 102