REVENUE - Contract Balances (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Change in contract liability
Beginning balance - Contract liability	$ 5,942	$ 2,679
Cash received in advance and not recognized as revenue	7,978	8,868
Amounts recognized as revenue as performance obligations satisfied	(12,380)	(8,222)
Ending balance - Contract liability	1,540	$ 3,325
Accrued expenses and other liabilities
Contract liabilities
Contract liabilities	$ 1,540		$ 5,942