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.



	September 30, 2015			December 31, 2014
	(in thousands)
Raw materials	$	36,571		$	34,153
Work in process	2,684			2,262
Finished goods	2,400			1,917
	41,655			38,332
Less: Allowance for excess and obsolete inventories	(603		)	(714		)
Total, net	$	41,052		$	37,618

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



	Three months ended					Nine months ended
	September 30, 2015			September 30, 2014		September 30, 2015			September 30, 2014
Allowance for excess and obsolete inventories:	(in thousands)
Balance, beginning of period	$	773		$	735	$	714		$	579
Provisions for excess and obsolete inventories	(35		)	67		24			223
Inventories written off	(135		)	—		(135		)	—
Balance, end of period	$	603		$	802	$	603		$	802