Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation (Summary of Stock Option Activity) (Details)

v3.8.0.1
Stock-Based Compensation (Summary of Stock Option Activity) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]        
Options outstanding, beginning, number of shares 2,151,542 2,288,870 2,640,785  
Granted, number of shares 540,537 430,544 500,761  
Cancelled, number of shares (246,450) (117,699) (172,018)  
Exercised, number of shares (675,742) (450,173) (680,658)  
Options outstanding, ending, number of shares 1,769,887 2,151,542 2,288,870 2,640,785
Options outstanding, beginning, weighted average exercise price $ 37.40 $ 32.69 $ 28.00  
Granted, weighted average exercise price 55.90 56.63 48.46  
Cancelled, weighted average exercise price 50.62 47.33 34.59  
Exercised, weighted average exercise price 29.52 29.25 25.63  
Options outstanding, ending, weighted average exercise price $ 44.22 $ 37.40 $ 32.69 $ 28.00
Options outstanding, beginning, weighted average remaining contractual life, years 6 years 8 months 8 days 6 years 4 months 22 days 6 years 6 months 6 years 6 months
Options outstanding, ending, weighted average remaining contractual life, years 6 years 8 months 8 days 6 years 4 months 22 days 6 years 6 months 6 years 6 months
Options outstanding, beginning, aggregate intrinsic value $ 45,253 $ 38,209 $ 43,682  
Options outstanding, ending, aggregate intrinsic value $ 48,962 $ 45,253 $ 38,209 $ 43,682
Options vested and expected to vest, number of shares 1,704,394      
Options vested and expected to vest, weighted average exercise price $ 43.77      
Options vested and expected to vest, weighted average remining contractual life, years 6 years 7 months 9 days      
Options vested and expected to vest, aggregate intrinsic value $ 47,904      
Options exercisable, number of shares 875,433      
Options exercisable, weighted average exercise price $ 34.17      
Options exercisable, weighted average remaining contractual life 4 years 11 months 12 days      
Options exercisable, aggregate intrinsic value $ 33,016