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SHARE-BASED COMPENSATION - Summary of SAR activity (Details) - Share appreciation rights - shares
shares in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Disclosure of terms and conditions of share-based payment arrangement [line items]    
Number of units, beginning of period (in shares) 674 533
Grants (in shares) 285 304
Exercises (in shares) (203) (36)
Forfeited (in shares) (160) (127)
Expired (in shares) (3) 0
Number of units, end of period (in shares) 593 674