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STOCK-BASED COMPENSATION - Employee Stock Purchase Plan - Additional Information (Details) - USD ($)
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Jun. 25, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Proceeds from common stock issued $ 567,000 $ 450,000 $ 999,000 $ 778,000  
Employee Stock Purchase Plan (ESPP) [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Reserved for issuance (in shares)         1,000,000
Purchase period (in months)       three-month  
Percentage of market value (in hundredths)       85.00%  
Maximum allocation of base compensation (in hundredths)     10.00%    
Maximum shares per purchase date (in shares)     12,500    
Maximum value per calendar year, per employee     $ 25,000    
Common stock issued (in shares)     4,105 5,467  
Proceeds from common stock issued     $ 787,000 $ 590,000  
Employee Stock Purchase Plan (ESPP) [Member] | Selling, General and Administrative Expense [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Charges to expense 35,000 37,000 58,000 59,000  
Employee Stock Purchase Plan (ESPP) [Member] | Research and Development Expense [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Charges to expense 58,000 44,000 95,000 72,000  
Employee Stock Purchase Plan (ESPP) [Member] | Cost of Sales [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Charges to expense $ 36,000 $ 37,000 $ 60,000 $ 56,000