Condensed Consolidated Statements of Income (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Condensed Consolidated Statements of Income (unaudited) [Abstract]
Net sales	$ 301,909	$ 294,394	$ 620,310	$ 573,116
Cost of sales	236,385	220,942	479,014	427,708
Gross profit	65,524	73,452	141,296	145,408
Selling, general, administrative and engineering expenses	44,220	44,961	97,342	88,766
Income from operations	21,304	28,491	43,954	56,642
Interest expense	185	326	450	793
Other income, net of expenses	261	276	773	819
Income from operations before income taxes	21,380	28,441	44,277	56,668
Income taxes	7,021	10,300	14,838	20,849
Net income	14,359	18,141	29,439	35,819
Net loss attributable to non-controlling interest	(61)	(51)	(101)	(116)
Net income attributable to controlling interest	$ 14,420	$ 18,192	$ 29,540	$ 35,935
Net income attributable to controlling interest:
Basic (in dollars per share)	$ 0.63	$ 0.79	$ 1.28	$ 1.56
Diluted (in dollars per share)	$ 0.62	$ 0.79	$ 1.27	$ 1.55
Weighted average number of common shares outstanding:
Basic (in shares)	23,026	22,999	23,020	22,982
Diluted (in shares)	23,183	23,135	23,179	23,135
Dividends declared per common share (in dollars per share)	$ 0.10	$ 0.10	$ 0.20	$ 0.20