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Income Taxes (Details) - USD ($)
$ in Millions
1 Months Ended 3 Months Ended 12 Months Ended
Dec. 31, 2017
Mar. 31, 2018
Mar. 31, 2017
Dec. 31, 2017
Effective tax rate        
Effective income tax rate (as a percent)   25.67% 30.10%  
Effect of Tax Cuts and Jobs Act of 2017        
Federal statutory tax rate   21.00%   35.00%
Provisional increase to deferred tax expense $ 261.3