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Share-Based Compensation (Narrative) (Details) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2018
Sep. 30, 2017
Sep. 30, 2018
Sep. 30, 2017
Share-Based Compensation [Line Items]        
Number of shares available for grant 880,465   880,465  
Share-based compensation expense $ 5,700,000 $ 5,600,000 $ 17,779,000 $ 16,057,000
Unamortized share-based compensation expense $ 30,900,000   $ 30,900,000  
Weighted average period over which unrecognized compensation cost is expected to be recognized     2 years 1 month 6 days  
Restricted Stock Units [Member]        
Share-Based Compensation [Line Items]        
Units granted     614,000 1,055,000
Weighted-average per share prices     $ 25.19 $ 30.03
Stock Options [Member]        
Share-Based Compensation [Line Items]        
Stock options awarded     579,000 530,000
Weighted-average exercise prices     $ 23.99 $ 24.64
Weighted average grant date fair value     $ 11.45 $ 13.11
Expected life     5 years 1 month 6 days  
Expected volatility     42.31%  
Risk-free rate     2.57%  
Quarterly dividends     $ 0  
Unrestricted Stock Units [Member]        
Share-Based Compensation [Line Items]        
Units granted     115,420 99,155
Weighted-average per share prices     $ 21.26 $ 26.26