Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Apr. 04, 2025	Mar. 29, 2024
Segment Reporting Information [Line Items]
Revenues	$ 145,507	$ 144,933
Compensation and related expenses	75,903	90,327
Operating Income	44,432	30,713
Capital Expenditures	1,252	1,509
Depreciation and Amortization	2,492	2,324
Operating segments
Segment Reporting Information [Line Items]
Compensation and related expenses	69,696	70,051
Operating Income	53,811	56,867
Capital Expenditures	537	446
Depreciation and Amortization	1,873	1,677
Corporate
Segment Reporting Information [Line Items]
Compensation and related expenses	6,207	20,276
Operating Income	(9,379)	(26,154)
Capital Expenditures	715	1,063
Depreciation and Amortization	619	647
Engineering and Other Scientific | Operating segments
Segment Reporting Information [Line Items]
Revenues	122,135	121,471
Compensation and related expenses	57,248	57,735
Operating Income	45,113	48,631
Capital Expenditures	475	417
Depreciation and Amortization	1,826	1,628
Environmental and Health | Operating segments
Segment Reporting Information [Line Items]
Revenues	23,372	23,462
Compensation and related expenses	12,448	12,316
Operating Income	8,698	8,236
Capital Expenditures	62	29
Depreciation and Amortization	$ 47	$ 49