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SHARE-BASED COMPENSATION - Summary of SAR activity (Details) - Share appreciation rights - shares
shares in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disclosure of terms and conditions of share-based payment arrangement [line items]    
Number of units, beginning of period (in shares) 593 674
Grants (in shares) 240 285
Exercises (in shares) (225) (203)
Forfeited (in shares) (57) (160)
Expired (in shares) (113) (3)
Number of units, end of period (in shares) 438 593