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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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Amount of excess tax benefit or (tax deficiency) associated with share-based compensation, which is included as a component of income tax provision on the income statement.

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Amount of the cumulative effect on retained earnings before related income tax effect.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
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Present value of lessee's discounted obligation for lease payments from operating lease.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
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