SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Rollforward of Contract Assets (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2019 USD ($)
Change in Contract with Customer Asset [Roll Forward]
Balance at December 31, 2018, current	$ 8,844
Balance at December 31, 2018, noncurrent	16,104
Amounts recognized as expense in the period	(9,899)
Balance at December 31, 2019, current	9,039
Balance at December 31, 2019, noncurrent	14,827
Balance at December 31, 2018	9,318
Revenue recognized that was included in the deferred revenue balance at December 31, 2018	(6,325)
Increases due to cash received, excluding amounts recognized as revenue during the period	4,215
Balance at December 31, 2019	7,208
Current
Change in Contract with Customer Asset [Roll Forward]
Balance at December 31, 2018, current	8,844
Deferred customer acquisition costs incurred in the period	1,790
Transition between short-term and long-term	8,304
Balance at December 31, 2019, current	9,039
Non-current
Change in Contract with Customer Asset [Roll Forward]
Balance at December 31, 2018, noncurrent	16,104
Deferred customer acquisition costs incurred in the period	7,027
Amounts recognized as expense in the period	0
Transition between short-term and long-term	(8,304)
Balance at December 31, 2019, noncurrent	$ 14,827