Annual report pursuant to Section 13 and 15(d)

Stock-Based Compensation (Options) (Details)

v3.8.0.1
Stock-Based Compensation (Options) (Details) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Total intrinsic value of options exercised $ 29,562 $ 14,165 $ 37,879  
Cash received from exercises of stock options 7,951 4,924 8,279  
Cash received from issuance of restricted stock $ 5 $ 6 $ 2  
Weighted-Average Remaining Contractual Life        
Outstanding 4 years 3 months 18 days 4 years 3 months 18 days 4 years 8 months 12 days 4 years 8 months 12 days
Options exercisable 3 years 9 months 18 days      
Aggregate Intrinsic Value        
Outstanding (in dollars) $ 69,939 $ 63,264 $ 61,199 $ 163,830
Options exercisable (in dollars) $ 66,291      
Stock options        
Options        
Outstanding at the beginning of the period (in shares) 3,033,194 3,533,791 4,265,337  
Granted (in shares) 75,238 163,864 358,087  
Exercised (in shares) (837,857) (598,382) (1,047,911)  
Forfeited (in shares) (16,010) (66,079) (41,722)  
Outstanding at the end of the period (in shares) 2,254,565 3,033,194 3,533,791 4,265,337
Options exercisable (in shares) 2,041,660      
Weighted-Average Exercise Price        
Outstanding at the beginning of the period (in dollars per share) $ 16.33 $ 15.03 $ 10.73  
Granted (in dollars per share) 31.70 22.38 48.38  
Exercised (in dollars per share) 9.49 8.23 7.90  
Forfeited (in dollars per share) 37.42 35.08 41.10  
Outstanding at the end of the period (in dollars per share) 19.23 16.33 15.03 $ 10.73
Options exercisable (in dollars per share) 17.74      
Aggregate Intrinsic Value        
Share Based Compensation Arrangement by Share Based Payment Award Options Outstanding Intrinsic Value Per Share $ 49.85 $ 35.25 $ 29.85  
Additional disclosures        
Unrecognized stock-based compensation expense related to unvested stock options $ 1,891      
Unrecognized compensation expense weighted-average recognition period 1 year 8 months 12 days      
Stock options | Minimum        
Additional disclosures        
Exercise prices of stock options outstanding (in dollars per share) $ 7.15      
Stock options | Maximum        
Additional disclosures        
Exercise prices of stock options outstanding (in dollars per share) $ 55.29