SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Allowances for Doubtful Accounts and Sales Adjustments (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	$ 4,647	$ 5,427	$ 3,396
Provisions for losses and sales adjustments - accounts receivable	1,636	(569)	2,031
Collection of accounts previously written off	(545)	(211)	0
Balance at end of year		4,647	$ 5,427
Accounts receivable, allowance for losses	$ 5,738	$ 4,647