REVENUE Deferred Revenue Activity (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Movement in Deferred Revenue [Roll Forward]
Deferred revenue at beginning of period	$ 99,259	$ 97,901
Billings deferred	46,686	39,334
Recognition of prior deferred revenue	(54,362)	(51,512)
Deferred revenue at end of period	91,583	85,723
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	45,100
Deferred Revenue	91,583	$ 85,723
Products
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	5,302
Subscription services
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	6,467
Maintenance contracts
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	71,266
Implied PCS
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	7,031
Professional services, training and other
Deferred Revenue Arrangement [Line Items]
Remaining Performance Obligation	$ 1,517