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REVENUE - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
REVENUE - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Deferred revenue	$ 22,400		$ 22,400		$ 600
Deferred revenue, revenue recognized during period	5	$ 200	200	$ 500
COVID-19
Disaggregation of Revenue [Line Items]
Deferred revenue	21,800		21,800
Variable consideration
Disaggregation of Revenue [Line Items]
Revenue recognized from changes in transaction prices	$ 500	$ 1,200	$ 9,100	$ 4,600