Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation (Stock Options) (Details)

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Stock-Based Compensation (Stock Options) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Total intrinsic value of options exercised $ 40,893 $ 15,667 $ 29,562  
Cash received from exercises of stock options $ 10,592 $ 5,305 $ 7,951  
Weighted-Average Exercise Price        
Granted (in dollars per share) $ 49.02      
Exercised (in dollars per share)     $ 9.49  
Forfeited (in dollars per share)     $ 37.42  
Weighted-Average Remaining Contractual Life        
Outstanding 3 years 4 months 24 days 3 years 4 months 24 days 4 years 3 months 18 days 4 years 3 months 18 days
Options exercisable 3 years 1 month 6 days      
Aggregate Intrinsic Value        
Outstanding $ 50,590 $ 56,046 $ 69,939 $ 63,264
Options exercisable $ 49,383      
Stock options        
Options        
Outstanding at the beginning of the period (in shares) 1,887,969 2,254,565 3,033,194  
Granted (in shares) 81,807 0 75,238  
Exercised (in shares) (783,216) (359,345) (837,857)  
Forfeited (in shares) (35,974) (7,251) (16,010)  
Outstanding at the end of the period (in shares) 1,150,586 1,887,969 2,254,565 3,033,194
Options exercisable (in shares) 1,097,503      
Weighted-Average Exercise Price        
Outstanding at the beginning of the period (in dollars per share) $ 20.05 $ 19.23 $ 16.33  
Granted (in dollars per share)   0 31.70  
Exercised (in dollars per share) 13.52 14.76    
Forfeited (in dollars per share) 48.33 27.51    
Outstanding at the end of the period (in dollars per share) 25.66 20.05 $ 19.23 $ 16.33
Options exercisable (in dollars per share) 24.63      
Share-based Compensation Arrangement by Share-based Payment Award, Additional General Disclosures [Abstract]        
Intrinsic value per share (in dollars per share) $ 69.63 $ 49.19   $ 49.85
Unrecognized stock-based compensation expense related to unvested stock options $ 793      
Unrecognized compensation expense weighted-average recognition period 1 year 10 months 24 days      
Stock options | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award, Additional General Disclosures [Abstract]        
Exercise prices of stock options outstanding (in dollars per share) $ 9.00      
Stock options | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award, Additional General Disclosures [Abstract]        
Exercise prices of stock options outstanding (in dollars per share) $ 55.29