SUPPLEMENTAL BALANCE SHEET INFORMATION

Allowance for Doubtful Accounts

Activity in the allowance for doubtful accounts is summarized as follows for the years ended December 31 (in thousands):



	2013			2012			2011
Balance, at beginning of year	$	2,953		$	3,077		$	2,536
Charged to expense	1,043			428			397
Write-offs and adjustments	(555		)	(552		)	144
Balance, at end of year	$	3,441		$	2,953		$	3,077

Costs and Estimated Earnings on Uncompleted Contracts

Costs and estimated earnings on uncompleted contracts consisted of the following at December 31 (in thousands):



	2013			2012
Costs incurred on uncompleted contracts	$	740,403		$	664,662
Estimated earnings to date	141,413			183,850
Subtotal	881,816			848,512
Less – billings to date	(826,795		)	(812,324		)
Total	$	55,021		$	36,188
Included in the accompanying balance sheets:
Costs and estimated earnings in excess of billings	79,999			67,740
Billings in excess of costs and estimated earnings	(24,978		)	(31,552		)
Total	$	55,021		$	36,188

Costs and estimated earnings in excess of billings represent work performed that could not be billed either due to contract stipulations or the required contractual documentation has not been finalized. Substantially all unbilled amounts are expected to be billed and collected within one year.

Inventories

Inventories are summarized as follows at December 31 (in thousands):



	2013		2012
Raw materials and supplies	$	19,680	$	16,250
Work-in-process	8,217		8,876
Finished products	12,518		18,056
Construction materials	18,353		15,941
Total	$	58,768	$	59,123

Property, Plant and Equipment

Property, plant and equipment consisted of the following at December 31 (in thousands):



	Estimated Useful Lives (Years)			2013			2012
Land and land improvements				$	11,964		$	11,437
Buildings and improvements	5	—	40	63,870			64,604
Machinery and equipment	4	—	10	185,307			177,383
Furniture and fixtures	3	—	10	25,848			16,933
Autos and trucks	3	—	10	52,145			50,119
Construction in progress				31,012			35,507
Subtotal				370,146			355,983
Less – Accumulated depreciation				(187,843		)	(172,820		)
Total				$	182,303		$	183,163

Depreciation expense was $28.0 million, $27.1 million and $28.6 million for the years ended December 31, 2013, 2012 and 2011, respectively.

Accrued Expenses

Accrued expenses consisted of the following at December 31 (in thousands):



	2013		2012
Vendor and other accrued expenses	$	36,778	$	32,394
Estimated casualty and healthcare liabilities	13,775		12,899
Job costs	13,843		14,077
Accrued compensation	15,942		12,943
Income tax payable and deferred income taxes	10,628		7,267
Total	$	90,966	$	79,580