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, 2016			December 31, 2015
	(in thousands)
Raw materials	$	36,152		$	33,853
Work in process	3,741			2,522
Finished goods	3,480			2,881
	43,373			39,256
Less: Allowance for excess and obsolete inventories	(894		)	(757		)
Total, net	$	42,479		$	38,499

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



	Three months ended
	March 31, 2016		March 31, 2015
Allowance for excess and obsolete inventories:	(in thousands)
Balance, beginning of period	$	757	$	714
Provisions for excess and obsolete inventories	137		41
Inventories written off	—		—
Balance, end of period	$	894	$	755