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Accounting Standards Update (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Accounting Policies [Abstract] |  |  |
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense | $ 4.5 | $ 2.7 | $ 6.6
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Diluted Earnings Per Share | $ 0.09 |  |
Excess Tax Benefit from Share-based Compensation, Operating Activities |  | $ 3.1 | $ 6.6
Allowance for fallouts | $ 1.5 |  |

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- Definition The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period. + References Reference 1: 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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