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Stock-based Compensation and Other Employee Benefit Plans Employee Benefit Plans (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Defined Benefit Plans and Other Postretirement Benefit Plans [Abstract] |  |  |
Deferred Compensation Plan Assets | $ 2.2 |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount | $ 7.5 | $ 5.6 | $ 7.6

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- Definition Defined Benefit Plans and Other Postretirement Benefit Plans [Abstract] + References No definition available. + Details
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- Definition Carrying amount as of the balance sheet date of assets held under deferred compensation agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
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