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Retirement Plans - Schedule of Net Periodic Benefit Cost Not yet Recognized (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
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United Kingdom Subsidiary | UK Plan |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Unrecognized losses | $ 102,054 | $ 102,943

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- Definition Amount, after tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=84228862&loc=SL7669686-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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