Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Consolidated Statements of Operations (unaudited) [Abstract]
Net sales	$ 304,802	$ 272,528	$ 630,582	$ 597,981
Cost of sales	221,352	271,420	470,606	518,868
Gross profit	83,450	1,108	159,976	79,113
Selling, general, administrative and engineering expenses	52,969	51,263	111,316	103,341
Income (loss) from operations	30,481	(50,155)	48,660	(24,228)
Interest expense	(484)	(168)	(1,131)	(318)
Other income, net of expenses	372	1,052	839	1,513
Income (loss) from operations before income taxes	30,369	(49,271)	48,368	(23,033)
Income tax provision (benefit)	7,008	(8,503)	10,789	(2,481)
Net income (loss)	23,361	(40,768)	37,579	(20,552)
Net loss attributable to non-controlling interest	16	94	72	145
Net income (loss) attributable to controlling interest	$ 23,377	$ (40,674)	$ 37,651	$ (20,407)
Net income (loss) attributable to controlling interest:
Basic (in dollars per share)	$ 1.04	$ (1.76)	$ 1.67	$ (0.89)
Diluted (in dollars per share)	$ 1.03	$ (1.76)	$ 1.66	$ (0.89)
Weighted average number of common shares outstanding:
Basic (in shares)	22,509	23,061	22,503	23,053
Diluted (in shares)	22,667	23,061	22,656	23,053
Dividends declared per common share (in dollars per share)	$ 0.11	$ 0.10	$ 0.22	$ 0.20