REVENUE Deferred Revenue Activity (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Movement in Deferred Revenue [Roll Forward]
Deferred revenue at beginning of period	$ 99,258	$ 97,901
Billings deferred	56,846	47,723
Recognition of prior deferred revenue	(69,337)	(64,460)
Deferred revenue at end of period	86,767	81,164
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	40,700
Deferred Revenue	86,767	$ 81,164
Products
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	4,364
Subscription services
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	7,380
Maintenance contracts
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	66,676
Implied PCS
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	6,400
Professional services, training and other
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	$ 1,947