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STOCK-BASED COMPENSATION - Narrative (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Restricted stock units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Granted (in shares)     170,613  
Fair value of units granted     $ 4,600,000  
Excess tax benefit for vested restricted stock $ 0 $ 0 0  
Performance stock units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Fair value of units granted   2,300,000 1,800,000  
LTIP        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares reserved for future issuance (in shares)       2,467,430
LTIP | Restricted stock units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Granted (in shares) 306,945      
Vesting period 3 years      
LTIP | Restricted stock units | Non-executive Board Members        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Fair value of units granted $ 4,900,000 $ 5,900,000 $ 6,200,000  
LTIP | Restricted stock units | Vesting Period One        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting percent of shares 33.00%      
LTIP | Restricted stock units | Vesting Period Two        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting percent of shares 33.00%      
LTIP | Restricted stock units | Vesting Period Three        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting percent of shares 33.00%      
LTIP | Performance stock units        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Granted (in shares) 83,209      
Fair value of units granted $ 1,900,000      
Distribution of shares to recipients (in shares) 0      
Vesting period 3 years      
Number of trading days 30 days      
TSR criterion percentage 67.00%      
ROCE criterion 33.00%      
LTIP | Performance stock units | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Ratio at which award holders get common stock of the company 0      
LTIP | Performance stock units | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Ratio at which award holders get common stock of the company 2      
LTIP | Stock options        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expiration period 10 years      
Granted (shares) 0 0 0