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Stock-Based Compensation - Restricted Stock Activity (Details) - Restricted Stock - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
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) 266,522    
Granted (in shares) 185,054 103,030  
Vested (in shares) (141,089)    
Forfeited (in shares) (12,690)    
Outstanding (in shares) 297,797 266,522  
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) $ 50.48    
Granted, weighted-average grant date fair value (in dollars per share) 46.90 $ 51.68 $ 42.91
Vested, weighted-average grant date fair value (in dollars per share) 51.09    
Forfeited, weighted-average grant date fair value (in dollars per share) 50.87    
Outstanding, weighted-average grant date fair value (in dollars per share) $ 47.95 $ 50.48  
Total compensation cost not yet recognized $ 9.1 $ 7.5  
Total compensation cost not yet recognized, period for recognition 2 years 6 months 2 years  
Total fair value of shares vested $ 6.5 $ 4.3 $ 6.6
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 3 years    
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Award vesting period 4 years