Segment Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Jan. 01, 2021	Jan. 03, 2020
Segment Reporting Information [Line Items]
Revenues	$ 466,269,000	$ 399,900,000	$ 417,199,000
Operating Income	108,927,000	83,249,000	85,111,000
Capital Expenditures	6,637,000	5,107,000	22,290,000
Depreciation and Amortization	6,487,000	6,871,000	6,806,000
Operating segments
Segment Reporting Information [Line Items]
Operating Income	168,352,000	127,344,000	137,411,000
Capital Expenditures	2,952,000	2,339,000	4,779,000
Depreciation and Amortization	4,224,000	4,435,000	5,033,000
Corporate
Segment Reporting Information [Line Items]
Operating Income	(59,425,000)	(44,095,000)	(52,300,000)
Capital Expenditures	3,685,000	2,768,000	17,511,000
Depreciation and Amortization	2,263,000	2,436,000	1,773,000
Engineering and Other Scientific | Operating segments
Segment Reporting Information [Line Items]
Revenues	380,909,000	319,346,000	339,796,000
Operating Income	140,400,000	100,616,000	110,822,000
Capital Expenditures	2,792,000	2,237,000	4,675,000
Depreciation and Amortization	4,031,000	4,239,000	4,827,000
Environmental and Health | Operating segments
Segment Reporting Information [Line Items]
Revenues	85,360,000	80,554,000	77,403,000
Operating Income	27,952,000	26,728,000	26,589,000
Capital Expenditures	160,000	102,000	104,000
Depreciation and Amortization	$ 193,000	$ 196,000	$ 206,000