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Recent Authoritative Accounting Guidance - New Accounting Pronouncements and Changes in Accounting Principles (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Reduction in income tax expense |  | $ 0.0
Accounting Standards Update 2016-02 [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Operating Lease, Right-of-Use Asset | $ 54.6 |
Operating Lease, Liability | 54.6 |
Accounting Standards Update 2018-02 | Adjustments for New Accounting Principle, Early Adoption |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Tax Cuts And Jobs Act Of 2017, Reclassification From AOCI To Retained Earnings | $ 3.1 |

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- Definition Amount of difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying domestic federal statutory income tax rate to pretax income (loss) from continuing operation, attributable to excess tax benefit for share-based compensation cost. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32687-109319 + Details
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