COMMITMENTS AND CONTINGENCIES (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended			36 Months Ended
	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Apr. 30, 2020	Dec. 31, 2017
Loss Contingencies [Line Items]
Long-term Purchase Commitment, Amount	$ 32,200				$ 3,000
Long-term Purchase Commitment, Period	5 years
Restructuring Reserve		$ 3,687	$ 157
Operating Leases, Income Statement, Sublease Revenue		800	1,300	$ 1,200
Operating Leases, Rent Expense, Net		10,200	10,300	9,500
Future minimum lease commitments under non-cancelable leases [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months		8,558
Operating Leases, Future Minimum Payments, Due in Two Years		7,259
Operating Leases, Future Minimum Payments, Due in Three Years		6,195
Operating Leases, Future Minimum Payments, Due in Four Years		5,383
Operating Leases, Future Minimum Payments, Due in Five Years		5,513
Operating Leases, Future Minimum Payments, Due Thereafter		11,776
Total		$ 44,684
Purchase Commitments [Abstract]
Maximum Purchase Commitment Period (in Years)		1 year
Aggregate total of non-cancelable purchase commitments		$ 9,000
Product warranty accrual [Roll Forward]
Accrual balance at beginning of year		1,337	1,706	2,545
Accruals for product warranties		1,065	973	858
Cost of warranty claims		(1,307)	(1,342)	(1,697)
Accrual balance at end of period		1,095	1,337	1,706
Facilities-Related [Member]
Loss Contingencies [Line Items]
Restructuring Reserve		0	$ 0	$ 318		$ 2,479
Standby Letters of Credit [Member] | Office Space - Burlington, Massachusetts [Member]
Loss Contingencies [Line Items]
Letters of Credit Outstanding, Amount		1,300
Loss Contingency, Range Of Possible Loss, Portion Not Accrued, Minimum		1,200
Minimum exposure		1,200
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		1,900
Operating Leases on Vacated Facilities [Member]
Loss Contingencies [Line Items]
Effect on Future Cash Flows, Amount		2,000
Aggregate obligation of vacated facilies		$ 2,000