CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Income Statement [Abstract]
Net sales	$ 157,489	$ 163,098	$ 318,056	$ 328,149
Cost of sales	97,290	102,437	197,349	205,063
Gross margin	60,199	60,661	120,707	123,086
Selling, general and administrative expenses	34,369	33,026	64,229	69,173
Research and development expenses	7,074	7,053	13,622	13,161
Operating income	18,756	20,582	42,856	40,752
Equity income in unconsolidated joint ventures	708	392	1,321	1,311
Other income (expense), net	191	(517)	(356)	(646)
Interest expense, net	(1,115)	(1,304)	(2,236)	(2,310)
Income before income tax expense	18,540	19,153	41,585	39,107
Income tax expense	13,163	5,599	21,280	11,910
Net income	$ 5,377	$ 13,554	$ 20,305	$ 27,197
Basic earnings per share (in dollars per share)	$ 0.30	$ 0.73	$ 1.13	$ 1.47
Diluted earnings per share (in dollars per share)	$ 0.29	$ 0.71	$ 1.11	$ 1.43
Shares used in computing:
Basic earnings per share (shares)	18,007	18,627	17,986	18,551
Diluted earnings per share (shares)	18,253	19,056	18,234	19,003