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Share-Based Compensation (Summary of Stock Option Activity) (Details) - $ / shares
 3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Shares [Roll Forward]    
Outstanding, beginning of period (in shares) 1,567,109  
Granted (in shares) 1,432,720  
Exercised (in shares) (79,081)  
Forfeited or Expired (in shares) (99,150)  
Outstanding, end of period (in shares) 2,821,598  
Exercisable, end of period (in shares) 560,848 359,656
Weighted Average Exercise Price [Roll Forward]    
Outstanding, beginning of period (weighted average exercise price) $ 25.27  
Granted (weighted average exercise price) 34.51  
Exercised (weighted average exercise price) 16.93  
Forfeited or Expired (weighted average exercise price) 33.84  
Outstanding, end of period (weighted average exercise price) 29.91  
Exercisable, end of period (weighted average exercise price) $ 18.67 $ 11.96