CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Net sales	$ 186,413	$ 174,879	$ 378,073	$ 340,366
Cost of sales	150,286	131,552	302,439	256,541
Gross profit	36,127	43,327	75,634	83,825
Selling, product development and administrative expenses	23,878	23,290	49,349	48,640
Operating income	12,249	20,037	26,285	35,185
Interest expense	572	795	1,112	1,401
Other (income) expense, net	(368)	792	(53)	1,125
Income before income taxes	12,045	18,450	25,226	32,659
Income tax expense	1,655	5,303	3,778	7,797
(Income) loss from equity method investment	(60)	22	(56)	68
Net income	$ 10,450	$ 13,125	$ 21,504	$ 24,794
Earnings per share:
Basic (USD per share)	$ 0.61	$ 0.77	$ 1.25	$ 1.46
Diluted (USD per share)	$ 0.60	$ 0.76	$ 1.24	$ 1.44
Weighted average number of common shares outstanding:
Basic (shares)	17,196	17,044	17,178	17,014
Diluted (shares)	17,335	17,262	17,334	17,272