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FAIR VALUE MEASUREMENT - Narrative (Details) - USD ($)
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Fair Value Disclosures [Abstract]      
Currency hedging cost for a year $ 0    
Currency hedging transactions, maximum term 1 year    
Derivative, amount of hedged item $ 0 $ 0 $ 0
Foreign exchange risk lien on checking account for bank guarantees granted to secure hedging transactions $ 300,000 300,000  
Foreign exchange risk lien on marketable securities for bank guarantees granted to secure hedging transactions   $ 300,000