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Stock-Based Compensation - Restricted Stock Activity (Details) - Restricted Stock [Member] - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting percentage per year 25.00%    
Period for share issuance after vesting 30 days    
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]      
Outstanding (in shares) 363,891    
Granted (in shares) 74,772 182,464  
Vested (in shares) (132,108)    
Forfeited (in shares) (11,875)    
Outstanding (in shares) 294,680 363,891  
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]      
Outstanding, weighted-average grant date fair value (in dollars per share) $ 38.83    
Granted, weighted-average grant date fair value (in dollars per share) 75.40 $ 55.14 $ 27.70
Vested, weighted-average grant date fair value (in dollars per share) 34.94    
Forfeited, weighted-average grant date fair value (in dollars per share) 55.45    
Outstanding, weighted-average grant date fair value (in dollars per share) $ 49.19 $ 38.83  
Total compensation cost not yet recognized $ 9.8 $ 10.6  
Total compensation cost not yet recognized, period for recognition 2 years 5 months 2 days 2 years 9 months 10 days  
Total fair value of shares vested $ 9.2 $ 6.5 $ 4.3