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FINANCIAL INSTRUMENTS (Details 3)
6 Months Ended 12 Months Ended
Jun. 30, 2018
USD ($)
customer
Dec. 31, 2016
customer
Dec. 31, 2017
USD ($)
Credit Risk      
Number of major customers | customer 3 3  
Amount of allowance for doubtful accounts | $ $ 0   $ 0
Accounts receivable | Credit risk | Major customer one      
Credit Risk      
Concentration risk (as a percent) 31.00% 35.00%  
Accounts receivable | Credit risk | Major customer two      
Credit Risk      
Concentration risk (as a percent) 28.00% 30.00%  
Accounts receivable | Credit risk | Major customer three      
Credit Risk      
Concentration risk (as a percent) 24.00% 27.00%