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SIGNIFICANT ACCOUNTING POLICIES - Primary Geographical Market (Details)
$ in Thousands
 3 Months Ended 12 Months Ended
Mar. 31, 2021
USD ($)
segment
Mar. 31, 2020
USD ($)
Dec. 31, 2020
USD ($)
segment
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Disaggregation of Revenue [Line Items]          
Number of operating segments | segment 1   1    
Number of Reportable Segments | segment 1   1    
Total revenues $ 100,606 $ 81,959 $ 345,592 $ 317,750 $ 260,135
Greater China          
Disaggregation of Revenue [Line Items]          
Total revenues 39,614 25,952 127,307 [1] 103,531 [1] 98,146 [1]
United States          
Disaggregation of Revenue [Line Items]          
Total revenues 8,053 15,934 38,729 69,016 49,997
All other countries          
Disaggregation of Revenue [Line Items]          
Total revenues $ 52,939 $ 40,073 $ 179,556 [2] $ 145,203 [2] $ 111,992 [2]
[1] Greater China is inclusive of mainland China, Hong Kong and Taiwan
[2] No single country included in the other countries category generated more than 10% of total revenue