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STOCK-BASED COMPENSATION - Employee Stock Purchase Plan - Additional Information (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Jun. 25, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Proceeds from common stock issued $ 1,159,000 $ 1,090,000 $ 944,000  
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) 3 months      
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) 7,492 10,303 9,730  
Proceeds from common stock issued $ 889,000 $ 798,000 $ 734,000  
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 79,000 82,000 69,000  
Employee Stock Purchase Plan (ESPP) [Member] | Cost of Sales [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Charges to expense 73,000 81,000 46,000  
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 $ 118,000 $ 130,000 $ 94,000