Segment Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Apr. 01, 2016	Apr. 03, 2015
Segment Reporting Information [Line Items]
Revenues	$ 83,156	$ 80,293
Operating Income	16,436	15,028
Capital Expenditures	1,481	627
Depreciation and Amortization	1,403	1,381
Operating segments
Segment Reporting Information [Line Items]
Operating Income	26,333	25,709
Capital Expenditures	1,213	416
Depreciation and Amortization	1,064	1,147
Engineering and Other Scientific
Segment Reporting Information [Line Items]
Revenues	64,810	59,801
Operating Income	21,138	19,245
Capital Expenditures	1,190	392
Depreciation and Amortization	1,021	1,104
Environmental and Health
Segment Reporting Information [Line Items]
Revenues	18,346	20,492
Operating Income	5,195	6,464
Capital Expenditures	23	24
Depreciation and Amortization	43	43
Corporate
Segment Reporting Information [Line Items]
Operating Income	(9,897)	(10,681)
Capital Expenditures	268	211
Depreciation and Amortization	$ 339	$ 234