NET EARNINGS (LOSS) PER SHARE - Potential Shares Not Included in the Computation of Diluted Earnings (Loss) Per Share (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential shares not included in the computation of diluted earnings (loss) per share	2,107	2,631	2,402
Restricted stock units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential shares not included in the computation of diluted earnings (loss) per share	0	477	0
Performance share units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential shares not included in the computation of diluted earnings (loss) per share	781	1,131	1,080