SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accounts Receivable and Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Activity in the entity's accounts receivable allowance
Balance at beginning of year	$ 4,549	$ 4,421
Provision charged to expense	2,083	2,608
Write-offs, less recoveries	(1,814)	(2,233)
Balance at end of year	4,962	$ 4,796
Adjustment | ASU 2016-13
Activity in the entity's accounts receivable allowance
Cumulative adjustment upon adoption of ASU 2016-13	$ 144