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Retirement Plans - Schedule of Weighted Average Assets Allocation and Weighted Average Target Allocation (Details) - United Kingdom Subsidiary - UK Plan | Dec. 31, 2017 | Dec. 31, 2016
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Defined Benefit Plan Disclosure [Line Items] |  |
Target Asset Allocation | 100.00% |
Asset Allocation | 100.00% | 100.00%
Equity securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Asset Allocation | 15.00% |
Asset Allocation | 14.10% | 44.90%
Debt securities |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Asset Allocation | 65.00% |
Asset Allocation | 77.30% | 55.00%
Cash |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Asset Allocation | 10.00% |
Asset Allocation | 8.60% | 0.10%
Property |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Target Asset Allocation | 10.00% |
Asset Allocation | 0.00% | 0.00%

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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 Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(5)(i) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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- Definition Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e2446-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920 + Details
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