Annual report pursuant to Section 13 and 15(d)

Share Based Compensation (Narrative) (Details)

v3.20.4
Share Based Compensation (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Additional compensation expense $ 6.4 $ 5.2 $ 4.0
Unrecognized compensation costs 14.3    
Compensation costs expected to be recognized in 2021 5.3    
Compensation costs expected to be recognized in 2022 $ 4.4    
Weighted average values of grants (in dollars per share) $ 21.33 $ 27.67 $ 29.72
Aggregate intrinsic value of exercised stock options $ 0.5 $ 2.5 $ 3.9
Weighted average remaining contractual term for total outstanding stock options 4 years 11 months 1 day    
Weighted average remaining contractual term for vested/exercisable stock options 3 years 8 months 8 days    
Aggregate intrinsic value of options outstanding $ 3.7    
Aggregate intrinsic value of vested/exercisable options outstanding 1.7    
Restricted Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Total grant date fair value of restricted stock vested $ 2.5 $ 1.2  
Employee Stock Options and Stock Options Issued for Services      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted average expected volatility 33.50% 28.20% 26.60%
Weighted average discount rates 0.55% 1.88% 2.78%
Expected lives 5 years 10 months 17 days 5 years 9 months 5 years 6 months 29 days
Employee Stock      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share-based payment award, number of additional shares authorized     300,000
Common stock authorized for grant (in shares) 900,000    
Exercise price per share of options granted, percentage, minimum 85.00%    
Employee common stock purchase plan, duration     10 years
Employee common stock purchase plan, offering period six    
Share Incentive Plans      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Share-based compensation arrangement by share-based payment award, number of additional shares authorized 900,000    
Share incentive plan, duration 10 years    
Common stock authorized for grant (in shares) 7,550,000    
Share Incentive Plans | Restricted Stock | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock and stock options vesting period 1 year    
Share Incentive Plans | Restricted Stock | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock and stock options vesting period 5 years    
Share Incentive Plans | Employee Stock Options and Stock Options Issued for Services      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Exercise price per share of options granted, percentage, minimum 100.00%    
Share Incentive Plans | Employee Stock Options and Stock Options Issued for Services | Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock and stock options vesting period 1 year    
Share Incentive Plans | Employee Stock Options and Stock Options Issued for Services | Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Restricted stock and stock options vesting period 5 years