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Goodwill and Identifiable Assets Goodwill (Details) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016
Goodwill [Roll Forward] |  |
Gross goodwill, period start | $ 873,513 | $ 874,906
Goodwill, Acquired During Period | 17,467 |
Translation adjustment | 3,115 | (1,393)
Gross goodwill, period end | 894,095 | 873,513
Apex |  |
Goodwill [Roll Forward] |  |
Gross goodwill, period start | (644,617) | 644,617
Translation adjustment |  | 0
Gross goodwill, period end | (662,084) | (644,617)
Apex | Stratacuity [Member] |  |
Goodwill [Roll Forward] |  |
Goodwill, Acquired During Period | 17,467 |
Oxford |  |
Goodwill [Roll Forward] |  |
Gross goodwill, period start | (228,896) | 230,289
Translation adjustment | 3,115 | (1,393)
Gross goodwill, period end | $ (232,011) | $ (228,896)

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- Definition Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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- Definition Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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- Definition Amount before 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a,h) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 + Details
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- Definition A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period. + References No definition available. + Details
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