SUMMARY OF SIGNIFICANT ACCOUNTING AND BUSINESS POLICIES - Changes in Allowance for Uncollectible Trade Accounts Receivables (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounts Receivable , Allowances for Credit Loss [Roll Forward]
Balance at beginning of year	$ 8,929	$ 10,126	$ 9,015
Charged to costs and expenses	1,194	139	2,368
Charged to other accounts	21	79	(86)
Deductions	(1,516)	(1,415)	(1,171)
Balance at end of year	$ 8,628	$ 8,929	$ 10,126