RECEIVABLES (Tables)

12 Months Ended

Dec. 31, 2021

Receivables [Abstract]

Summary of Accounts Receivable

A summary of accounts receivable as of December 31, 2021 and 2020 is as follows (in thousands): 

	December 31,
	2021		2020
Trade accounts receivable	$	161,751	$	157,513
Unbilled revenues	35,933		46,471
Allowance for credit losses	(8,912)		(9,918)
Total	$	188,772	$	194,066

Summary of Activity in Allowance for Doubtful Accounts

The following table shows a rollforward of the allowance for credit losses:

	Twelve Months Ended December 31,
	2021		2020		2019
Balance at beginning of period	$	9,918	$	9,990	$	15,182
Adoption of account pronouncement ASC 3261	—		1,410		—
Provision for expected credit losses	2,193		1,612		(2,573)
Write-offs	(3,143)		(3,193)		(2,673)
Foreign exchange effects	(56)		99		54
Balance at end of period	$	8,912	$	9,918	$	9,990

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