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DERIVATIVE FINANCIAL INSTRUMENTS - Currency Risk Management (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
U S Dollar Call Options    
Disclosure of detailed information about financial instruments [line items]    
Notional amount $ 0 $ 0
2019    
Disclosure of detailed information about financial instruments [line items]    
Non-hedge derivatives $ 626,400