SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Accounts Receivable and Allowance for Credit Losses (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Activity in the entity's accounts receivable allowance
Balance at beginning of year	$ 4,549	$ 4,421
Provision charged to expense	4,565	4,879
Write-offs, less recoveries	(3,290)	(3,897)
Balance at end of year	5,968	$ 5,403
Adjustment | ASU 2016-13
Activity in the entity's accounts receivable allowance
Cumulative adjustment upon adoption of ASU 2016-13	144
Cumulative adjustment to retained earnings	(300)
Decrease in value of partnership interests	$ 200