Business Acquisitions Business Acquisitions - Early Discovery Pro Forma Information (Details) - Early Discovery UK - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	6 Months Ended
Jun. 27, 2015	Jun. 28, 2014	Jun. 27, 2015	Jun. 28, 2014
Business Acquisition [Line Items]
Revenue	$ 339,573	$ 341,179	$ 659,987	$ 665,656
Net income attributable to common shareholders	$ 48,509	$ 35,264	$ 80,050	$ 65,688
Earnings per common share
Basic (in dollars per share)	$ 1.04	$ 0.75	$ 1.71	$ 1.40
Diluted (in dollars per share)	$ 1.02	$ 0.74	$ 1.68	$ 1.38

Business Acquisition, Pro Forma Earnings Per Share, Basic and Diluted [Abstract]

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- Definition

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.

+ References

No definition available.

+ Details

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- Definition

The pro forma basic net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(2)-(3)

-URI http://asc.fasb.org/extlink&oid=56956515&loc=d3e1392-128463

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The pro forma diluted net income per share for a period as if the business combination or combinations had been completed at the beginning of a period.

+ References

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The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

+ References

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The pro forma revenue for a period as if the business combination or combinations had been completed at the beginning of the period.

+ References

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