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Share-Based Compensation (Narrative) (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Share-Based Compensation [Line Items]        
Number of shares available for grant 684,598   684,598  
Expected life     5 years 1 month 6 days  
Expected volatility     42.31%  
Risk-free rate     2.57%  
Quarterly dividends     $ 0  
Share-based compensation expense $ 6,000,000 $ 6,100,000 12,063,000 $ 10,420,000
Unamortized share-based compensation expense $ 36,400,000   $ 36,400,000  
Weighted average period over which unrecognized compensation cost is expected to be recognized     2 years 2 months 12 days  
Restricted Stock Units [Member]        
Share-Based Compensation [Line Items]        
Units granted     614,000 665,000
Weighted-average per share prices     $ 25.19 $ 30.48
Stock Options [Member]        
Share-Based Compensation [Line Items]        
Stock options awarded     579,000 265,000
Weighted-average exercise prices     $ 23.73 $ 23.47
Weighted average grant date fair value     $ 11.45 $ 13.70
Unrestricted Stock Units [Member]        
Share-Based Compensation [Line Items]        
Units granted     115,420 99,155
Weighted-average per share prices     $ 21.26 $ 26.26