CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Income Statement [Abstract]
Net sales	$ 165,259	$ 160,366	$ 483,314	$ 488,515
Cost of sales	103,330	100,694	300,678	305,757
Gross margin	61,929	59,672	182,636	182,758
Selling, general and administrative expenses	31,489	29,190	95,718	98,363
Research and development expenses	7,294	7,285	20,916	20,446
Operating income	23,146	23,197	66,002	63,949
Equity income in unconsolidated joint ventures	898	877	2,220	2,187
Other income (expense), net	676	(756)	320	(1,404)
Interest expense, net	(811)	(1,126)	(3,047)	(3,435)
Income before income tax expense	23,909	22,192	65,495	61,297
Income tax expense	7,844	9,646	29,125	21,555
Net income	$ 16,065	$ 12,546	$ 36,370	$ 39,742
Basic earnings per share (in dollars per share)	$ 0.89	$ 0.68	$ 2.02	$ 2.15
Diluted earnings per share (in dollars per share)	$ 0.88	$ 0.67	$ 2.00	$ 2.10
Shares used in computing:
Basic earnings per share (shares)	17,996	18,430	17,990	18,511
Diluted earnings per share (shares)	18,183	18,650	18,217	18,885