Quarterly report pursuant to Section 13 or 15(d)

Stock-Based Compensation (Options) (Details)

v3.10.0.1
Stock-Based Compensation (Options) (Details) - Stock options - USD ($)
$ / shares in Units, $ in Thousands
 3 Months Ended 9 Months Ended 12 Months Ended
Sep. 30, 2018
Jun. 30, 2018
Mar. 31, 2018
Sep. 30, 2018
Dec. 31, 2017
Options          
Outstanding at the beginning of the period (in shares) 2,077,874 2,090,040 2,254,565 2,254,565  
Exercised (in shares) (174,445) (12,166) (162,857)    
Forfeited (in shares) (5,583)   (1,668)    
Outstanding at the end of the period (in shares) 1,897,846 2,077,874 2,090,040 1,897,846 2,254,565
Options exercisable (in shares) 1,820,156     1,820,156  
Weighted-Average Exercise Price          
Outstanding at the beginning of the period (in dollars per share) $ 19.62 $ 19.57 $ 19.23 $ 19.23  
Exercised (in dollars per share) 15.25 11.42 14.76    
Forfeited (in dollars per share) 0.00   32.46    
Outstanding at the end of the period (in dollars per share) 20.00 $ 19.62 $ 19.57 20.00 $ 19.23
Options exercisable (in dollars per share) $ 19.64     $ 19.64  
Weighted-Average Remaining Contractual Life          
Outstanding 3 years 7 months 6 days 3 years 10 months 24 days 4 years 1 month 6 days   4 years 3 months 18 days
Options exercisable       3 years 6 months  
Aggregate Intrinsic Value          
Outstanding (in dollars) $ 77,726 $ 73,421 $ 78,859 $ 77,726 $ 69,939
Options exercisable (in dollars) 75,194     75,194  
Share-based Compensation Arrangement by Share-based Payment Award, Additional General Disclosures [Abstract]          
Unrecognized stock-based compensation expense related to unvested stock options $ 887     $ 887  
Unrecognized compensation expense weighted-average recognition period       1 year 2 months 12 days  
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     $ 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     $ 55.29