SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Changes in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of year	$ 665	$ 869	$ 951
Provision	282	63	119
Write-offs, net of recoveries	(277)	(267)	(201)
Balance at end of year	$ 670	$ 665	$ 869