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Income Taxes - Narrative (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Income Tax Disclosure [Abstract]      
Tax expense $ 3.9 $ 1.5  
Federal income tax at statutory rate (as a percent) 21.00%    
Unrecognized tax benefits $ 19.6   $ 19.5