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Employee Compensation and Benefit Plans - Schedule of Stock Option Activity (Footnote) (Details) - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Jan. 16, 2015
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock options granted, fair value (in dollars per share)       $ 3.28
Total intrinsic value of stock options exercised     $ 0.1 $ 0.3
Shares delivered by employees as payment for the exercise price and income tax withholdings on compensation (in shares)       56,013
Shares issued related to exercise of stock options (in shares)       89,664
Market-based options that have not met performance criteria (in shares)   280,000    
Average common stock trading price to determine market condition for options exercise   $ 32.24    
Net aggregate intrinsic value of stock options outstanding   $ 0.0    
Net aggregate intrinsic value of stock options exercisable   $ 0.0    
Market-based options outstanding (in shares)   4,662,814    
Market-based options outstanding, exercisable (in shares)   4,382,814    
Weighted average remaining contractual term of options outstanding   1 year 11 months 8 days    
Weighted average remaining contractual term of options exercisable   1 year 6 months 29 days    
Total fair value of stock options vested and became exercisable   $ 0.7 $ 1.1 $ 2.0
Former Executive Chairman Of Board Of Directors [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Stock options vested 500,000