Accounts Receivable

6 Months Ended

Jun. 30, 2011

Accounts Receivable [Abstract]

Accounts Receivable

4. Accounts Receivable

Accounts receivable consist of billed and unbilled amounts at June 30, 2011 and December 31, 2010, as follows:

	As of:
	June 30,		December 31,
	2011		2010
	(in thousands)
Billed receivables	$	42,452	$	51,611
Unbilled receivables:
Billable receivables at end of period		52,744		61,500
Other		34,914		20,280
Total unbilled receivables		87,658		81,780
Total accounts receivable		130,110		133,391
Less: allowance for doubtful accounts		590		698
Total accounts receivable, net	$	129,520	$	132,693

Other unbilled receivables primarily consist of amounts that will be billed upon milestone completions and other accrued amounts that cannot be billed as of the end of the period. Substantially all other unbilled receivables are expected to be billed and collected within the next 12 months.