Condensed Consolidated Statements of Income (unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Condensed Consolidated Statements of Income (unaudited) [Abstract]
Net sales	$ 268,042	$ 277,256	$ 556,791	$ 515,929
Cost of sales	205,809	215,078	428,512	396,994
Gross profit	62,233	62,178	128,279	118,935
Selling, general, administrative and engineering expenses	43,308	40,247	87,112	83,672
Income from operations	18,925	21,931	41,167	35,263
Other income:
Interest expense	420	109	717	182
Other income, net of expenses	273	729	2,033	1,544
Income from operations before income taxes	18,778	22,551	42,483	36,625
Income taxes	7,120	8,061	15,909	12,589
Net income	11,658	14,490	26,574	24,036
Net loss attributable to non-controlling interest	(147)	(7)	(335)	(6)
Net income attributable to controlling interest	$ 11,805	$ 14,497	$ 26,909	$ 24,042
Net income attributable to controlling interest
Basic (in dollars per share)	$ 0.51	$ 0.64	$ 1.17	$ 1.05
Diluted (in dollars per share)	$ 0.51	$ 0.63	$ 1.16	$ 1.04
Weighted average number of common shares outstanding:
Basic (in shares)	22,942	22,822	22,923	22,804
Diluted (in shares)	23,119	23,099	23,117	23,101
Dividends declared per common share (in dollars per share)	$ 0.10	$ 0.10	$ 0.20	$ 0.20