REVENUE RECOGNITION - Summary of Significant Changes in Unbilled Receivables and Deferred Liabilities Balances (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Deferred Revenue (Increase) Decrease
Balance	$ (162,301)	$ (144,862)
Revenue recognized that was previously included in deferred revenue	145,535	97,556
Increases due to cash received	(160,021)	(144,200)
Cumulative catch-up adjustment arising from changes in estimates of transaction price, net	9,854	1,458
Net change	(4,632)	(45,186)
Balance	(166,933)	(190,048)
Unbilled Receivables Increase (Decrease)
Balance	10,429	1,362
Unbilled receivables recognized, net	24,209	13,494
Transferred to receivables from unbilled receivables	(7,147)
Net change	17,062	13,494
Balance	$ 27,491	$ 14,856