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Basis of Presentation Summary of Significant Accounting Policies - Textual (Details) - Accounting Standards Update 2016-09 [Member] - USD ($)
$ in Millions
3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2017
Sep. 30, 2017
Sep. 30, 2016
Dec. 31, 2016
New Accounting Pronouncements or Change in Accounting Principle [Line Items]        
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense $ 0.4 $ 9.0    
Excess Tax Benefit from Share-based Compensation, Operating Activities       $ 17.3
Taxes paid on behalf of employees for shares withheld     $ 9.9