8. Detail of Certain Balance Sheet Accounts

Activity in our allowance for doubtful accounts consists of the following (in thousands):

	December 31,

	2012			2011			2010
Balance at beginning of year	$	4,615		$	5,029		$	7,200
Additions for bad debt expense		2,753			214			340
Deductions for uncollectible receivables written off, net of recoveries		(1,090	)		(770	)		(2,689	)
Allowance for doubtful accounts of acquired companies at date of acquisition		55			142			178

Balance at end of year	$	6,333		$	4,615		$	5,029

Other current liabilities consist of the following (in thousands):

	December 31,

	2012		2011
Accrued warranty costs	$	6,781	$	8,234
Accrued job losses		2,137		1,777
Accrued rent and lease obligations		673		2,793
Accrued sales and use tax		1,710		1,494
Deferred revenue		1,143		1,592
Liabilities due to former owners		2,349		—
Other current liabilities		12,284		13,959

	$	27,077	$	29,849

Contracts in progress are as follows (in thousands):

	December 31,

	2012			2011
Costs incurred on contracts in progress	$	1,182,085		$	1,071,406
Estimated earnings, net of losses		134,534			132,096
Less—Billings to date		(1,364,229	)		(1,247,535	)

	$	(47,610	)	$	(44,033	)

Costs and estimated earnings in excess of billings	$	26,204		$	26,602
Billings in excess of costs and estimated earnings		(73,814	)		(70,635	)

	$	(47,610	)	$	(44,033	)