Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation (Options) (Details)

v3.19.1
Stock-Based Compensation (Options) (Details) - Stock options - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Options    
Outstanding at the beginning of the period (in shares) 1,887,969  
Granted (in shares) 81,807  
Exercised (in shares) (200,326)  
Forfeited (in shares) (1,100)  
Outstanding at the end of the period (in shares) 1,768,350 1,887,969
Options exercisable (in shares) 1,655,119  
Weighted-Average Exercise Price    
Outstanding at the beginning of the period (in dollars per share) $ 20.05  
Granted (in dollars per share) 49.02  
Exercised (in dollars per share) 16.91  
Forfeited (in dollars per share) 31.70  
Outstanding at the end of the period (in dollars per share) 21.74 $ 20.05
Options exercisable (in dollars per share) $ 20.23  
Weighted-Average Remaining Contractual Life    
Outstanding 3 years 6 months 3 years 4 months 24 days
Options exercisable 3 years 1 month 6 days  
Aggregate Intrinsic Value    
Outstanding (in dollars) $ 77,197 $ 56,046
Options exercisable (in dollars) 74,744  
Share-based Compensation Arrangement by Share-based Payment Award, Additional General Disclosures [Abstract]    
Unrecognized stock-based compensation expense related to unvested stock options $ 2,050  
Unrecognized compensation expense weighted-average recognition period 2 years 6 months  
Minimum    
Share-based Compensation Arrangement by Share-based Payment Award, Additional General Disclosures [Abstract]    
Exercise prices of stock options outstanding (in dollars per share) $ 7.15  
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