STOCK-BASED COMPENSATION - Employee Stock Purchase Plan - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 25, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from common stock issued	$ 1,523,000	$ 1,159,000	$ 1,090,000
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)	9,668	7,492	10,303
Proceeds from common stock issued	$ 1.2	$ 889,000	$ 798,000
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	96,000	79,000	82,000
Employee Stock Purchase Plan (ESPP) [Member] | Cost of Sales [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Charges to expense	111,000	73,000	81,000
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	$ 139,000	$ 118,000	$ 130,000