4.	Receivables

Our receivables principally relate to contracts with the U.S. government and prime contractors or subcontractors of the U.S. government. The components of contract receivables are presented in the table below.

	September 30, 2016			December 31, 2015
Billed receivables	$	95,228		$	229,358
Unbilled receivables		271,805			163,882
Allowance for doubtful accounts		(11,758	)		(11,480	)
Total receivables, net	$	355,275		$	381,760

The billed receivables at December 31, 2015 reflect a one week acceleration of our billing cycle to invoice contractually billable work in anticipation of the consolidation of our financial systems in early January 2016. This resulted in an increase in our billed receivables, with a corresponding decrease in our unbilled receivables, of approximately $110 million. The balances as of September 30, 2016 reflect a return to our normal billing cycles.