CONTINGENCIES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Product warranty accrual [Roll Forward]
Accrual balance at beginning of year	$ 1,095	$ 1,337
Accruals for product warranties	466	384
Cost of warranty claims	(374)	(357)
Accrual balance at end of period	1,187	$ 1,364
Standby Letters of Credit [Member] | Office Space - Burlington, Massachusetts [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	700
Loss Contingency, Range Of Possible Loss, Portion Not Accrued, Minimum	700
Standby Letters of Credit [Member] | Office Space - Other Facilities [Member]
Loss Contingencies [Line Items]
Letters of Credit Outstanding, Amount	600
Standby Letters of Credit [Member] | Other Operating Obligations [Member]
Loss Contingencies [Line Items]
Letters of Credit Outstanding, Amount	1,600
Research and Development Arrangement [Member]
Loss Contingencies [Line Items]
Long-term Purchase Commitment, Amount	$ 32,200
Long-term Purchase Commitment, Period	5 years
Other Inventory, Purchased Goods, Gross	$ 5,100