CONDENSED CONSOLIDATED STATEMENTS OF INCOME (LOSS) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Statement [Abstract]
Net sales	$ 163,098	$ 153,495	$ 328,149	$ 300,135
Cost of sales	102,509	96,357	205,205	189,078
Gross margin	60,589	57,138	122,944	111,057
Selling and administrative expenses	33,026	34,499	69,173	62,097
Research and development expenses	7,053	6,420	13,161	11,283
Operating income	20,510	16,219	40,610	37,677
Equity income in unconsolidated joint ventures	392	1,062	1,311	2,039
Other income (expense), net	(517)	(76)	(646)	(1,268)
Interest expense, net	(1,304)	(720)	(2,310)	(1,468)
Income before income tax expense	19,081	16,485	38,965	36,980
Income tax expense	5,541	5,583	11,798	11,498
Net income	$ 13,540	$ 10,902	$ 27,167	$ 25,482
Basic earnings per share (in dollars per share)	$ 0.73	$ 0.60	$ 1.46	$ 1.41
Diluted earnings per share (in dollars per share)	$ 0.71	$ 0.58	$ 1.43	$ 1.37
Shares used in computing:
Basic net income per share (shares)	18,627	18,158	18,551	18,055
Diluted net income per share (shares)	19,056	18,689	19,003	18,619