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Description of Business and Summary of Significant Accounting Policies Description of Business and Summary of Significant Accounting Policies (Recent Accounting Pronouncements) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Jan. 01, 2019
Accounting Standards Update 2016-09 [Member] |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Income tax deficiencies from share-based awards |  | $ 4.3 |
Cumulative effect to reduce retained earnings (pre-tax), share-based accounting standard |  | $ 0.2 |
Scenario, Forecast [Member] | Subsequent Event [Member] | Accounting Standards Update 2014-09 [Member] | Minimum [Member] |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect to increase retained earnings (after-tax), revenue recognition standard | $ 9.0 |  |
Scenario, Forecast [Member] | Subsequent Event [Member] | Accounting Standards Update 2014-09 [Member] | Maximum [Member] |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Cumulative effect to increase retained earnings (after-tax), revenue recognition standard | $ 12.0 |  |
Scenario, Forecast [Member] | Subsequent Event [Member] | Accounting Standards Update 2016-02 [Member] | Minimum [Member] |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Expected additional operating lease liabilities |  |  | $ 375.0
Scenario, Forecast [Member] | Subsequent Event [Member] | Accounting Standards Update 2016-02 [Member] | Maximum [Member] |  |  |
New Accounting Pronouncements or Change in Accounting Principle [Line Items] |  |  |
Expected additional operating lease liabilities |  |  | $ 475.0

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