Inventories

Inventories are valued at the lower of cost or market. Cost is determined by the first-in, first-out (“FIFO”) method. We establish an allowance for excess and obsolete inventories based on product line changes, the feasibility of substituting parts and the need for supply and replacement parts.



	March 31, 2014			December 31, 2013
	(in thousands)
Raw materials	$	32,085		$	28,592
Work in process	2,474			2,286
Finished goods	915			1,841
	35,474			32,719
Less: Allowance for excess and obsolete inventories	(583		)	(579		)
Total, net	$	34,891		$	32,140

The related changes in the allowance for excess and obsolete inventories account are as follows:



	Three months ended
	March 31, 2014		March 31, 2013
Allowance for excess and obsolete inventories:	(in thousands)
Balance, beginning of period	$	579	$	363
Provisions for excess and obsolete inventories	4		196
Inventories written off	—		(27		)
Balance, end of period	$	583	$	532