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Stock-Based Compensation (Summary of Unvested Restricted Stock Units, Activity) (Details) - Restricted stock units [Member] - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Unvested, number, beginning of period 396,198    
Unvested, weighted average grant date fair value, beginning of period $ 40.51    
Granted, number 276,499    
Granted, weighted average grant date fair value $ 51.98 $ 45.15 $ 33.38
Forfeited, number (33,274)    
Forfeited, weighted average grant date fair value $ 47.20    
Expired, number (3,500)    
Expired, weighted average grant date fair value $ 23.13    
Vested, number (170,528)    
Vested, weighted average grant date fair value $ 39.04    
Unvested, number, end of period 465,395 396,198  
Unvested, weighted average grant date fair value, end of period $ 47.51 $ 40.51  
Unvested, weighted average remaining contractual term 7 years 6 months    
Unvested, aggregate intrinsic value [1] $ 29,785    
[1] The intrinsic value is calculated as the market value as of the end of the fiscal period.