Consolidated Statements of Income - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net sales	$ 1,139,447	$ 969,236	$ 1,025,272
Cost of sales	927,953	785,773	834,492
Gross margin	211,494	183,463	190,780
Selling, general, and administrative expense	146,170	129,683	129,941
Research and development expense	13,981	12,802	12,796
Other - net	12,764	13,874	2,775
Operating profit	38,579	27,104	45,268
Interest expense - net	2,183	1,789	2,450
Income before income taxes	36,396	25,315	42,818
Income tax (benefit) expense	24,945	(425)	10,660
Net income	$ 11,451	$ 25,740	$ 32,158
Basic earnings per share:
Net income per share of common stock (in usd per share)	$ 0.57	$ 1.29	$ 1.60
Diluted earnings per share:
Net income per share of common stock (in usd per share)	0.56	1.27	1.58
Cash dividends per share	$ 0.395	$ 0.375	$ 0.355
Weighted-average number of shares of common stock outstanding:
Basic	20,027	19,983	20,097
Diluted	20,415	20,213	20,402