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Coworker Retirement and Other Compensation Benefits - Coworker Stock Purchase Plan (Details) - USD ($) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Coworker Retirement and Other Compensation Benefits [Line Items] |  |  |
Equity-based compensation expense | $ 43,700,000 | $ 39,200,000 | $ 31,200,000
Coworker Stock Purchase Plan |  |  |
Coworker Retirement and Other Compensation Benefits [Line Items] |  |  |
Employee stock purchase plan discount to market price (as percent) | 5.00% |  |
Equity-based compensation expense | $ 0 |  |

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- Definition [Line Items] for Coworker Retirement and Other Compensation Benefits [Table] + References No definition available. + Details
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- Definition Employee Stock Purchase Plan, discount to market price, percent + References No definition available. + Details
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- Definition Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 14.F) -URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5047-113901 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (h)(1)(i) -URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901 + Details
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- Details
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