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Stockholders' Equity - Share Grants Activity (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Weighted average grant date fair value      
Granted (in dollars per share) $ 64.11 $ 48.52 $ 37.99
Restricted stock      
Number of Shares      
Share grants outstanding, beginning balance (in shares) 529,465    
Granted (in shares) 257,175    
Acquired (in shares) 0    
Vested or exercised (in shares) (212,355)    
Share grants outstanding, ending balance (in shares) 574,285 529,465  
Weighted average grant date fair value      
Share grants outstanding, beginning balance (in dollars per share) $ 37.34    
Granted (in dollars per share) 64.11    
Acquired (in dollars per share) 0.00    
Vested or exercised (in dollars per share) 37.77    
Share grants outstanding, ending balance (in dollars per share) $ 49.68 $ 37.34  
Options      
Number of Shares      
Share grants outstanding, beginning balance (in shares) 0    
Granted (in shares) 0    
Acquired (in shares) 270,710    
Vested or exercised (in shares) (108,903)    
Share grants outstanding, ending balance (in shares) 161,807 0  
Weighted average grant date fair value      
Share grants outstanding, beginning balance (in dollars per share) $ 0.00    
Granted (in dollars per share) 0.00    
Acquired (in dollars per share) 36.48    
Vested or exercised (in dollars per share) 34.11    
Share grants outstanding, ending balance (in dollars per share) $ 38.08 $ 0.00