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Income Taxes - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended
Sep. 30, 2018
Dec. 31, 2017
Income Tax Disclosure [Abstract]    
Unrecognized tax benefits that, if recognized, would impact effective tax rate $ 9.7 $ 10.7
Accrued interest and penalties payable related to unrecognized tax benefits 1.4 $ 1.6
Estimated decrease in gross unrecognized tax positions within the next 12 months, maximum 3.9  
Reduction in tax expense from change in federal tax rate $ 5.3  
Reduction of effective income tax rate 5.00%