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REVENUE - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Disaggregation of Revenue [Line Items]          
Deferred revenue $ 18,700   $ 18,700   $ 25,000
Deferred revenue, revenue recognized during period 200 $ 5 24,600 $ 200  
COVID-19          
Disaggregation of Revenue [Line Items]          
Deferred revenue 17,800   17,800    
Deferred revenue, revenue recognized during period 100   24,300    
Variable consideration          
Disaggregation of Revenue [Line Items]          
Revenue recognized (downward adjustments) from changes in transaction prices $ (200) $ 500 $ (13,200) $ 9,100