RECEIVABLES - Allowance for Credit Losses (Details) - USD ($) $ in Thousands		9 Months Ended	12 Months Ended
		Sep. 30, 2021	Dec. 31, 2020
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period		$ 9,918	$ 9,990
Provision for expected credit losses		1,985	1,612
Write-offs		(2,859)	(3,193)
Foreign exchange effects		(70)	99
Balance at end of period		8,974	9,918
Cumulative Effect, Period of Adoption, Adjustment | Accounting Standards Update 2016-13
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at beginning of period	[1]	$ 0	1,410
Balance at end of period	[1]		$ 0

[1] Due to the initial adoption of ASC 326 as of January 1, 2020.