SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Contracts (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($)
Current
Change in Contract with Customer Asset [Roll Forward]
Contract assets - current	$ 0
Adjustments resulting from adoption of ASC 606	9,035
Deferred customer acquisition costs incurred in the period	1,877
Amounts recognized as expense in the period	(9,638)
Reclassification between short-term and long-term	7,570
Contract assets - current	8,844
Non-current
Change in Contract with Customer Asset [Roll Forward]
Contract assets - non-current	0
Adjustments resulting from adoption of ASC 606	16,313
Deferred customer acquisition costs incurred in the period	7,361
Amounts recognized as expense in the period	0
Reclassification between short-term and long-term	(7,570)
Contract assets - non-current	$ 16,104