Goodwill Reported By segment (Detail) - USD ($) $ in Thousands	Dec. 28, 2018	Dec. 29, 2017
Goodwill Reported By Segment [Line Items]
Goodwill	$ 8,607	$ 8,607
Engineering and Other Scientific [Member]
Goodwill Reported By Segment [Line Items]
Goodwill	508
Environmental and Health [Member]
Goodwill Reported By Segment [Line Items]
Goodwill	$ 8,099

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant