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Stock Incentive Plans - Summary of Restricted Common Stock and Performance-based Restricted Units (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Restricted Common Stock      
Number of shares or units      
Unvested at the beginning of year(in shares) 752,701    
Granted (in shares) 429,752    
Vested (in shares) (741,690)    
Forfeited (in shares) (65,946)    
Unvested at the end of year (in shares) 374,817 752,701  
Weighted Average Grant Date Fair Value      
Unvested at the beginning of year(in dollars per share) $ 11.90    
Granted (in dollars per share) 13.05 $ 12.58 $ 9.70
Vested (in dollars per share) (12.18)    
Forfeited (in dollars per share) (11.77)    
Unvested at the end of year (in dollars per share) $ 12.68 $ 11.90  
Vested (in shares) 741,690    
Restricted Common Stock | Accelerated Vesting      
Number of shares or units      
Vested (in shares) (200,797)    
Weighted Average Grant Date Fair Value      
Vested (in shares) 200,797    
Compensation expense $ 2.4    
Restricted Stock Units      
Number of shares or units      
Unvested at the beginning of year(in shares) 776,500    
Granted (in shares) 409,800    
Vested (in shares) (366,400)    
Forfeited (in shares) (68,400)    
Unvested at the end of year (in shares) 751,500 776,500  
Weighted Average Grant Date Fair Value      
Unvested at the beginning of year(in dollars per share) $ 10.66    
Granted (in dollars per share) 12.64    
Vested (in dollars per share) (9.22)    
Forfeited (in dollars per share) (11.03)    
Unvested at the end of year (in dollars per share) $ 12.41 $ 10.66  
Vested (in shares) 366,400