Condensed Consolidated Statements of Operations (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Condensed Consolidated Statements of Operations (unaudited) [Abstract]
Net sales	$ 256,613	$ 252,054	$ 854,595	$ 872,364
Cost of sales	198,329	212,970	717,197	691,985
Gross profit	58,284	39,084	137,398	180,379
Selling, general, administrative and engineering expenses	51,054	45,494	154,396	142,836
Income (loss) from operations	7,230	(6,410)	(16,998)	37,543
Interest expense	170	188	488	638
Other income, net of expenses	23	1,113	1,536	1,886
Income (loss) from operations before income taxes	7,083	(5,485)	(15,950)	38,791
Income tax provision (benefit)	180	(2,782)	(2,301)	12,055
Net income (loss)	6,903	(2,703)	(13,649)	26,736
Net loss attributable to non-controlling interest	(92)	(36)	(238)	(137)
Net income (loss) attributable to controlling interest	$ 6,995	$ (2,667)	$ (13,411)	$ 26,873
Net income (loss) attributable to controlling interest:
Basic (in dollars per share)	$ 0.31	$ (0.12)	$ (0.58)	$ 1.17
Diluted (in dollars per share)	$ 0.30	$ (0.12)	$ (0.58)	$ 1.16
Weighted average number of common shares outstanding:
Basic (in shares)	22,923	23,029	23,009	23,023
Diluted (in shares)	23,084	23,029	23,009	23,180
Dividends declared per common share (in dollars per share)	$ 0.11	$ 0.10	$ 0.31	$ 0.30