Net accounts receivable and billing in excess of costs on uncompleted contracts consisted of the following at September 30, 2012, and October 2, 2011:

	Fiscal Year Ended

	September 30, 2012			October 2, 2011
	(in thousands)

Billed	$	362,331		$	364,779
Unbilled		355,793			309,091
Contract retentions		17,908			15,553

Total accounts receivable – gross		736,032			689,423
Allowance for doubtful accounts		(35,552	)		(32,244	)

Total accounts receivable – net	$	700,480		$	657,179

Current billings in excess of costs on uncompleted contracts	$	90,909		$	84,754
Non-current billings in excess of costs on uncompleted contracts		4,410			5,832

Total billings in excess of costs on uncompleted contracts	$	95,319		$	90,586

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 September 30, 2012 are expected to be billed and collected within 12 months. Unbilled accounts receivable at September 30, 2012 and October 2, 2011, include approximately $21 million and $16 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 collection is deemed to have changed. No material losses were recognized related to the collectability of claims during fiscal 2012 and 2011. 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 were reported as part of our "Other long-term liabilities" on our consolidated balance sheets.

Billed accounts receivable related to U.S. federal government contracts were $65.9 million and $88.5 million at September 30, 2012 and October 2, 2011, respectively. U.S. federal government unbilled receivables, net of progress payments, were $100.4 million and $102.7 million at September 30, 2012 and October 2, 2011, respectively. Other than the U.S. federal government, no single client accounted for more than 10% of our accounts receivable at September 30, 2012 and October 2, 2011.