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Stock-based Compensation Plans and Awards - Stock-based Compensation Expense - Additional Information (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Income tax benefit related to stock-based compensation included in net income (loss) $ 0.0 $ 0.0  
Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Capitalized stock-based compensation expense $ 0.4 0.4 $ 0.4
Sold | Cracked      
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]      
Accelerated compensation cost   $ 0.8