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CREDIT RISK AND CONCENTRATION (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Concentration Risk      
Increase or decrease in interest rates of short-term investments that will not significantly affect the fair value of investment portfolio (as a percent) 10.00%    
Cash, Cash Equivalents and Short Term Investments | Countries Other than US | Credit Concentration Risk      
Concentration Risk      
Cash and cash equivalents and short-term investments $ 51.0 $ 46.0  
Accounts Receivable | Customer Concentration Risk | Customer A      
Concentration Risk      
Concentration of risk (as a percent) 1.00% 2.00%  
Accounts Receivable | Customer Concentration Risk | Customer B      
Concentration Risk      
Concentration of risk (as a percent) 93.00% 87.00%  
Sales Revenue, Net | Customer Concentration Risk | Customer A      
Concentration Risk      
Concentration of risk (as a percent) 28.00% 40.00% 50.00%
Sales Revenue, Net | Customer Concentration Risk | Customer B      
Concentration Risk      
Concentration of risk (as a percent) 58.00% 39.00% 35.00%
Subsidiaries | Cash, Cash Equivalents and Short Term Investments | China | Credit Concentration Risk      
Concentration Risk      
Cash and cash equivalents and short-term investments $ 8.9 $ 7.9