CONTINGENCIES (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020	Sep. 30, 2019
Product warranty accrual [Roll Forward]
Accrual balance at beginning of year		$ 1,337	$ 1,706
Accruals for product warranties		1,030	732
Cost of warranty claims		(1,003)	(1,016)
Accrual balance at end of period	$ 1,364	1,364	$ 1,422
Standby Letters of Credit [Member] | Office Space - Burlington, Massachusetts [Member]
Loss Contingencies [Line Items]
Loss Contingency, Range of Possible Loss, Portion Not Accrued	1,300	1,300
Loss Contingency, Range Of Possible Loss, Portion Not Accrued, Minimum	1,200	1,200
Standby Letters of Credit [Member] | Office Space - Other Facilities [Member]
Loss Contingencies [Line Items]
Letters of Credit Outstanding, Amount	600	600
Standby Letters of Credit [Member] | Other Operating Obligations [Member]
Loss Contingencies [Line Items]
Letters of Credit Outstanding, Amount	1,900	1,900
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	$ 600	$ 600