Segment Information - Sales to External Customers and Gross Profit (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 29, 2015	Mar. 30, 2014
Segment Reporting Information [Line Items]
Sales to external customers	$ 220,816us-gaap_SalesRevenueNet	$ 226,264us-gaap_SalesRevenueNet
Gross profit	105,271us-gaap_GrossProfit	106,324us-gaap_GrossProfit
Industry [Member]
Segment Reporting Information [Line Items]
Sales to external customers	111,900	106,437
Gross profit	56,610	56,132
Science [Member]
Segment Reporting Information [Line Items]
Sales to external customers	108,916	119,827
Gross profit	$ 48,661	$ 50,192
Top 10 Customers [Member]
Segment Reporting Information [Line Items]
Concentration Risk, Customer	35.00%	30.00%

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 825

-SubTopic 10

-Section 50

-Paragraph 21

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-URI http://asc.fasb.org/extlink&oid=49121117&loc=d3e13537-108611

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

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-Name Accounting Standards Codification

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

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- Definition

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

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-Name Accounting Standards Codification

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- Definition

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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