2. Accounts Receivable – Net

Net accounts receivable and billings in excess of costs on uncompleted contracts consisted of the following:

	March 31, 2013		September 30, 2012
	(in thousands)

Billed	$	351,897	$	362,331
Unbilled	343,416		355,793
Contract retentions	28,012		17,908
Total accounts receivable – gross	723,325		736,032

Allowance for doubtful accounts	(36,205)		(35,552)
Total accounts receivable – net	$	687,120	$	700,480

Current billings in excess of costs on uncompleted contracts	$	79,131	$	90,909
Non-current billings in excess of costs on uncompleted contracts	1,474		4,410
Total billings in excess of costs on uncompleted contracts	$	80,605	$	95,319

Billed accounts receivable represent amounts billed to clients that have not been collected. Unbilled accounts receivable represent revenue recognized but not yet billed pursuant to contract terms or billed after the period end date. Most of our unbilled receivables at March 31, 2013 are expected to be billed and collected within 12 months. Unbilled accounts receivable at March 31, 2013 and September 30, 2012 include approximately $36 million and $21 million, respectively, related to claims and requests for equitable adjustment on contracts that provide for price redetermination, primarily with U.S. federal government agencies. These amounts are management’s estimate of the most probable amount to be realized upon the conclusion of the claims settlement process. We regularly evaluate these claim amounts and record appropriate adjustments to operating earnings when collectability is deemed to have changed. No losses were recognized related to the collectability of claims during the second quarter and first half of fiscal 2013 and 2012. Contract retentions represent amounts withheld by clients until certain conditions are met or the project is completed, which may be several months or years. The allowance for doubtful accounts is determined based on a review of client-specific accounts, and contract issues resulting from current events and economic circumstances. Billings in excess of costs on uncompleted contracts represent the amount of cash collected from clients and billings to clients on contracts in advance of revenue recognized. The majority of billings in excess of costs on uncompleted contracts will be earned within 12 months. The non-current billings in excess of costs on uncompleted contracts are reported as part of our “Other long-term liabilities” on our condensed consolidated balance sheets.

Billed accounts receivable related to U.S. federal government contracts were $66.4 million and $65.9 million at March 31, 2013 and September 30, 2012, respectively. U.S. federal government unbilled receivables, net of progress payments, were $83.4 million and $100.4 million at March 31, 2013 and September 30, 2012, respectively. Other than the U.S. federal government, no single client accounted for more than 10% of our accounts receivable at March 31, 2013 and September 30, 2012.