REVENUE - Deferred Revenue (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Movement in Deferred Revenue [Roll Forward]
Deferred revenue, beginning of the period	$ 51,804	$ 44,331
Deferred revenue, end of the period	54,726	47,046
Revenue recognized in the period from amounts included in deferred revenue at the beginning of the period	$ 18,933	$ 15,570