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Income Taxes (Details) - USD ($)
$ in Millions
6 Months Ended 12 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Dec. 31, 2017
Income Taxes [Abstract]      
Statutory corporate tax rate 21.00%   35.00%
Effective tax rate 25.70% 37.40%  
Excess tax expense (benefit) from vested stock awards and state income taxes $ 0.1 $ (0.2)