Segment Information - Sales to External Customers and Gross Profit (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 27, 2015	Sep. 28, 2014	Sep. 27, 2015	Sep. 28, 2014
Segment Reporting Information [Line Items]
Sales to external customers	$ 212,561	$ 227,756	$ 657,566	$ 690,976
Gross profit	104,277	108,581	321,653	324,756
Industry [Member]
Segment Reporting Information [Line Items]
Sales to external customers	105,280	107,058	336,760	340,722
Gross profit	55,184	55,101	176,541	175,321
Science [Member]
Segment Reporting Information [Line Items]
Sales to external customers	107,281	120,698	320,806	350,254
Gross profit	$ 49,093	$ 53,480	$ 145,112	$ 149,435
Top 10 Customers [Member]
Segment Reporting Information [Line Items]
Concentration Risk, Customer	32.00%	31.80%	29.90%	29.20%

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=51801978&loc=d3e6351-108592

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Aggregate revenue less cost of goods and services sold or operating expenses directly attributable to the revenue generation activity.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

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-Subparagraph (SX 210.5-03.1,2)

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Total revenue from sale of goods and services rendered during the reporting period, in the normal course of business, reduced by sales returns and allowances, and sales discounts.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

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-Section S99

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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