Segment Information (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended
Sep. 27, 2013	Sep. 28, 2012	Sep. 27, 2013	Sep. 28, 2012
Segment Reporting Information [Line Items]
Revenues	$ 75,231	$ 73,298	$ 223,396	$ 219,707
Operating income	15,160	14,728	43,604	43,905
Capital expenditures	892	1,483	4,593	3,425
Depreciation and amortization	1,283	1,133	3,667	3,459
Engineering and other scientific
Segment Reporting Information [Line Items]
Revenues	56,395	53,071	163,353	158,784
Operating income	18,115	16,217	51,747	47,573
Capital expenditures	664	1,103	3,924	2,039
Depreciation and amortization	813	677	2,269	2,061
Environmental and health
Segment Reporting Information [Line Items]
Revenues	18,836	20,227	60,043	60,923
Operating income	5,624	6,933	19,104	20,722
Capital expenditures	41	174	110	348
Depreciation and amortization	76	72	221	209
Operating segments
Segment Reporting Information [Line Items]
Operating income	23,739	23,150	70,851	68,295
Capital expenditures	705	1,277	4,034	2,387
Depreciation and amortization	889	749	2,490	2,270
Corporate
Segment Reporting Information [Line Items]
Operating income	(8,579)	(8,422)	(27,247)	(24,390)
Capital expenditures	187	206	559	1,038
Depreciation and amortization	$ 394	$ 384	$ 1,177	$ 1,189

The current period expense charged against earnings on long-lived, physical assets not used in production, and which are not intended for resale, to allocate or recognize the cost of such assets over their useful lives; or to record the reduction in book value of an intangible asset over the benefit period of such asset; or to reflect consumption during the period of an asset that is not used in production.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

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- Definition

The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 13

-Subparagraph (c)

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Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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