REVENUE - Deferred Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Movement in Deferred Revenue [Roll Forward]
Deferred revenue, beginning of the period	$ 36,451	$ 1,590
Deferred revenue, end of the period	44,331	36,451
Deferred revenue arising from business combination	0	22,800
Revenue recognized in the period from amounts included in deferred revenue at the beginning of the period	31,510	1,590
Balances without adoption of ASC 606
Movement in Deferred Revenue [Roll Forward]
Deferred revenue, beginning of the period		5,893
ASU 2014-09 | Effect of change
Movement in Deferred Revenue [Roll Forward]
Deferred revenue, beginning of the period	$ 0	(4,303)
Deferred revenue, end of the period		$ 0