Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 27, 2024	Sep. 29, 2023	Sep. 27, 2024	Sep. 29, 2023
Segment Reporting Information [Line Items]
Revenues	$ 136,279	$ 133,336	$ 421,748	$ 413,866
Operating Income	25,847	33,933	92,304	92,928
Capital Expenditure	2,226	1,814	4,742	17,242
Depreciation and Amortization	2,389	2,361	7,199	6,535
Operating segments
Segment Reporting Information [Line Items]
Operating Income	47,839	46,209	155,729	143,614
Capital Expenditure	887	566	1,843	3,349
Depreciation and Amortization	1,785	1,803	5,282	4,583
Corporate
Segment Reporting Information [Line Items]
Operating Income	(21,992)	(12,276)	(63,425)	(50,686)
Capital Expenditure	1,339	1,248	2,899	13,893
Depreciation and Amortization	604	558	1,917	1,952
Engineering and Other Scientific | Operating segments
Segment Reporting Information [Line Items]
Revenues	115,244	110,857	355,193	344,552
Operating Income	40,292	38,734	132,687	121,064
Capital Expenditure	887	541	1,769	3,210
Depreciation and Amortization	1,735	1,750	5,128	4,428
Environmental and Health | Operating segments
Segment Reporting Information [Line Items]
Revenues	21,035	22,479	66,555	69,314
Operating Income	7,547	7,475	23,042	22,550
Capital Expenditure	0	25	74	139
Depreciation and Amortization	$ 50	$ 53	$ 154	$ 155