Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Condensed Consolidated Statements of Operations (unaudited) [Abstract]
Net sales	$ 272,528	$ 301,909	$ 597,981	$ 620,310
Cost of sales	271,420	236,385	518,868	479,014
Gross profit	1,108	65,524	79,113	141,296
Selling, general, administrative and engineering expenses	51,263	44,220	103,341	97,342
Income (loss) from operations	(50,155)	21,304	(24,228)	43,954
Interest expense	168	185	318	450
Other income, net of expenses	1,052	261	1,513	773
Income (loss) from operations before income taxes	(49,271)	21,380	(23,033)	44,277
Income tax provision (benefit)	(8,503)	7,021	(2,481)	14,838
Net income (loss)	(40,768)	14,359	(20,552)	29,439
Net loss attributable to non-controlling interest	(94)	(61)	(145)	(101)
Net income (loss) attributable to controlling interest	$ (40,674)	$ 14,420	$ (20,407)	$ 29,540
Net income (loss) attributable to controlling interest:
Basic (in dollars per share)	$ (1.76)	$ 0.63	$ (0.89)	$ 1.28
Diluted (in dollars per share)	$ (1.76)	$ 0.62	$ (0.89)	$ 1.27
Weighted average number of common shares outstanding:
Basic (in shares)	23,061	23,026	23,053	23,020
Diluted (in shares)	23,061	23,183	23,053	23,179
Dividends declared per common share (in dollars per share)	$ 0.10	$ 0.10	$ 0.20	$ 0.20