RECEIVABLES (Tables)

12 Months Ended

Dec. 31, 2019

Receivables [Abstract]

Summary of Accounts Receivable

A summary of accounts receivable as of December 31, 2019 and 2018 is as follows (in thousands):

	December 31,
	2019			2018
Trade accounts receivable	$	192,743		$	207,266
Unbilled revenues	62,864			76,268
Allowance for doubtful accounts	(9,990		)	(15,182		)
Total	$	245,617		$	268,352

Summary of Activity in Allowance for Doubtful Accounts

The following summarizes the activity in the allowance for doubtful accounts (in thousands):

	Twelve Months Ended December 31,
	2019			2018			2017
Balance at beginning of period	$	15,182		$	11,308		$	7,835
Provision for doubtful accounts	(2,573		)	11,662			7,097
Write-off of bad debts	(2,619		)	(7,788		)	(3,624		)
Balance at end of period	$	9,990		$	15,182		$	11,308