Inventories

Inventories are valued at the lower of cost or net realizable value. 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, 2018			December 31, 2017
	(in thousands)
Raw materials	$	65,694		$	57,784
Work in process	6,116			5,957
Finished goods	8,486			8,163
	80,296			71,904
Less: Allowance for excess and obsolete inventories	(1,114		)	(1,118		)
Total, net	$	79,182		$	70,786

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



	Three months ended						Nine months ended
	September 30, 2018			September 30, 2017			September 30, 2018			September 30, 2017
Allowance for excess and obsolete inventories:	(in thousands)
Balance, beginning of period	$	1,407		$	1,642		$	1,118		$	1,382
Provisions for excess and obsolete inventories	(263		)	(206		)	55			54
Inventories written off	(30		)	(243		)	(59		)	(243		)
Balance, end of period	$	1,114		$	1,193		$	1,114		$	1,193