Receivables

12 Months Ended

May 31, 2013

Receivables

3. RECEIVABLES

A summary of accounts receivable as of May 31, 2013 and 2012 is as follows (in thousands):

	May 31,
	2013			2012
Trade accounts receivable	$	152,030		$	141,469
Unbilled revenues		25,516			20,561
Allowance for doubtful accounts		(5,438	)		(4,405	)
Total	$	172,108		$	157,625

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 as of May 31, 2013, 2012 and 2011 (in thousands):

	Twelve Months Ended May 31,
	2013			2012			2011
Balance at beginning of year	$	4,405		$	4,222		$	4,934
Provision for doubtful accounts		2,922			1,650			1,048
Write-off of bad debts		(1,889	)		(1,467	)		(1,760	)
Balance at end of year	$	5,438		$	4,405		$	4,222