REVENUE Deferred Revenue Activity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021
Movement in Deferred Revenue [Roll Forward]
Deferred revenue at beginning of period	$ 99,259	$ 97,901
Billings deferred	31,132	28,687
Recognition of prior deferred revenue	(32,885)	(31,176)
Deferred revenue at end of period	97,506	95,412
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation			$ 49,500
Deferred Revenue	$ 97,506	$ 95,412	97,506
Products
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation			6,852
Subscription services
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation			5,718
Maintenance contracts
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation			75,174
Implied PCS
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation			7,652
Professional services, training and other
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation			$ 2,110