SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Allowance for credit losses (Details) - Trade Accounts Receivable - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Beginning balance	$ 5,246	$ 771	$ 757
Provision for credit loss expense	1,088	5,716	1,664
Write-offs	(3,113)	(1,730)	(2,156)
Recoveries	522	489	506
Total ending allowance balance	$ 3,743	$ 5,246	$ 771