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CURRENT AND NON-CURRENT EMPLOYEE BENEFITS - Assumptions (Details) - Y
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Assumptions    
Discount rate 2.70% 2.70%
Expected salary increase rate 2.00% 2.00%
Turnover rate 5.40% 5.40%
Retirement age of women 60 60
Retirement age of men 65 65