Segment Information (Detail) - USD ($)	12 Months Ended
	Dec. 30, 2022	Dec. 31, 2021	Jan. 01, 2021
Segment Reporting Information [Line Items]
Revenues	$ 513,293,000	$ 466,269,000	$ 399,900,000
Operating Income	140,842,000	108,927,000	83,249,000
Capital Expenditures	12,647,000	6,637,000	5,107,000
Depreciation and Amortization	7,079,000	6,487,000	6,871,000
Operating segments
Segment Reporting Information [Line Items]
Operating Income	180,019,000	168,352,000	127,344,000
Capital Expenditures	4,835,000	2,952,000	2,339,000
Depreciation and Amortization	4,660,000	4,224,000	4,435,000
Corporate
Segment Reporting Information [Line Items]
Operating Income	(39,177,000)	(59,425,000)	(44,095,000)
Capital Expenditures	7,812,000	3,685,000	2,768,000
Depreciation and Amortization	2,419,000	2,263,000	2,436,000
Engineering and Other Scientific | Operating segments
Segment Reporting Information [Line Items]
Revenues	427,796,000	380,909,000	319,346,000
Operating Income	152,679,000	140,400,000	100,616,000
Capital Expenditures	4,661,000	2,792,000	2,237,000
Depreciation and Amortization	4,489,000	4,031,000	4,239,000
Environmental and Health | Operating segments
Segment Reporting Information [Line Items]
Revenues	85,497,000	85,360,000	80,554,000
Operating Income	27,340,000	27,952,000	26,728,000
Capital Expenditures	174,000	160,000	102,000
Depreciation and Amortization	$ 171,000	$ 193,000	$ 196,000