RECEIVABLES

12 Months Ended

Dec. 31, 2017

Receivables [Abstract]

RECEIVABLES

RECEIVABLES

A summary of accounts receivable as of December 31, 2017 and December 31, 2016 is as follows (in thousands):

	December 31,
	2017			2016
Trade accounts receivable	$	244,133		$	230,889
Unbilled revenues	69,138			39,719
Allowance for doubtful accounts	(11,308		)	(7,835		)
Total	$	301,963		$	262,773

The allowance for doubtful accounts is our best estimate of the amount of probable credit losses in our existing accounts receivable. Account balances are charged off against the allowance after all means of collection have been exhausted and the potential for recovery is remote. The following summarizes the activity in the allowance for doubtful accounts (in thousands):

	Twelve Months Ended December 31,						Seven Months Ended December 31,			Twelve Months Ended May 31,
	2017			2016			2015			2015
Balance at beginning of period	$	7,835		$	3,548		$	2,775		$	4,784
Provision for doubtful accounts	7,097			6,336			1,819			233
Write-off of bad debts	(3,624		)	(2,049		)	(1,046		)	(2,242		)
Balance at end of period	$	11,308		$	7,835		$	3,548		$	2,775