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Employee Benefit Plans (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
U.S. |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer contributions to plan | $ 26.2 | $ 17.4 | $ 15.2
U.K. |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Employer contributions to plan | $ 9.2 | $ 7.3 | $ 7.7

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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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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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- Details
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- Details
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