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Income Taxes (Narrative) (Details) - USD ($)
$ in Millions
 6 Months Ended 12 Months Ended
Dec. 22, 2017
Jun. 30, 2018
Dec. 31, 2017
Income Tax Disclosure [Abstract]      
Doubling Bonus Depreciation 100.00%    
Doubling bonus depreciation, period 5 years    
Additional depreciation     $ 5.0
Income tax benefit   $ 0.6  
Expected effective income tax rate for the year   27.00%