Annual report pursuant to Section 13 and 15(d)

STOCK???BASED COMPENSATION - Additional Information (Details)

v3.20.4
STOCK‑BASED COMPENSATION - Additional Information (Details)
$ in Millions
12 Months Ended
Mar. 16, 2017
installment
shares
Jul. 19, 2016
installment
shares
Jun. 14, 2013
shares
Dec. 31, 2020
USD ($)
shares
Dec. 31, 2019
USD ($)
shares
Dec. 31, 2018
USD ($)
shares
Oct. 22, 2020
shares
Mar. 31, 2017
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Options granted (in shares) | shares       0 0 0    
Options, outstanding, intrinsic value       $ 14.6        
Options, exercisable, intrinsic value       $ 14.6        
Exercised (in shares) | shares       0        
Term for outstanding stock       2 years 6 months        
Remaining contractual term       2 years 4 months 24 days        
Compensation cost not yet recognized, period for recognition       1 year 9 months 18 days        
Tax benefit from compensation expense       $ 9.1 $ 7.8 $ 5.5    
Compensation not yet recognized, stock options       11.1        
Stock options                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Options granted (in shares) | shares 793,738 1,274,549 2,799,408          
Award vesting rights     25.00%          
Expiration period 10 years 10 years 10 years          
Number of installments | installment 4 5            
Stock-based compensation       2.3 0.5 0.6    
Stock options | Former Officer                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock-based compensation       2.0        
Restricted stock units                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock-based compensation       $ 5.1 3.5 2.9    
Granted (in shares) | shares       1,185,832        
Vesting period       3 years        
Restricted stock units, conversion of stock, conversion rights (in shares) | shares       1        
Compensation not yet recognized, other than options       $ 5.9        
Compensation cost not yet recognized, period for recognition       1 year 9 months 18 days        
Restricted stock units | Former Officer                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock-based compensation       $ 0.1        
Performance stock units                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock-based compensation       $ 1.7 $ 3.8 $ 2.0    
Granted (in shares) | shares       1,007,058        
Percentage of outstanding stock minimum       0.00%        
Percentage of outstanding stock maximum       200.00%        
Performance stock units | Former Officer                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Stock-based compensation       $ 0.1        
2017 Incentive Award Plan                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares authorized (in shares) | shares               5,800,000
2020 Long Term Incentive Plan                
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                
Number of shares authorized (in shares) | shares             4,650,000