CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Net sales	$ 191,660	$ 165,487
Cost of sales	152,153	124,989
Gross profit	39,507	40,498
Selling, product development and administrative expenses	25,471	25,350
Operating income	14,036	15,148
Interest expense	540	606
Other expense, net	315	333
Income before income taxes	13,181	14,209
Income tax expense	2,123	2,494
Loss from equity method investment	4	46
Net income	$ 11,054	$ 11,669
Earnings per share:
Basic (USD per share)	$ 0.64	$ 0.69
Diluted (USD per share)	$ 0.64	$ 0.68
Weighted average number of common shares outstanding:
Basic (shares)	17,164	16,983
Diluted (shares)	17,339	17,284