RECEIVABLES (Tables)

12 Months Ended

Dec. 31, 2020

Receivables [Abstract]

Summary of Accounts Receivable

A summary of accounts receivable as of December 31, 2020 and 2019 is as follows (in thousands): 

	December 31,
	2020		2019
Trade accounts receivable	$	157,513	$	192,743
Unbilled revenues	46,471		62,864
Allowance for credit losses	(9,918)		(9,990)
Total	$	194,066	$	245,617

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,
	2020		2019		2018
Balance at beginning of period	$	9,990	$	15,182	$	11,308
Adoption of account pronouncement ASC 3261	1,410		—		—
Provision for expected credit losses	1,612		(2,573)		11,662
Write-offs	(3,193)		(2,673)		(7,475)
Foreign exchange effects	99		54		(313)
Balance at end of period	$	9,918	$	9,990	$	15,182

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